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Theoretical Investigation of X-Ray Absorption near Edge Spectroscopy (XANES) Angular Dependence of Aligned Carbon Nanotubes Grown by DC HF CVD Process

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Materials Sciences and Applications 2015年第5期6卷 373-390页

作者： Bridinette Thiodjio Sendja Rolant Eba Medjo Jeannot Mane Mane Germain Hubert Ben-Bolie pierre owono ateba Ecole Nationale Supérieure Polytechnique (National Advanced School of Engineering) Department of Mathematics and Physical Sciences University of Yaoundé I Yaounde Cameroon Physics Department Faculty of Science University of Douala Douala Cameroon Physics Department Faculty of Science University of Yaoundé I Yaounde Cameroon

Carbon nanotubes (CNTs) grown on plain substrates SiO2/Si(100) by a direct current and hot filaments catalytic chemical vapor deposition process have been studied by synchrotron X-ray absorption near edge spectroscopy (XANES) technique to theoretically investigate the angular-dependence of carbone (C) K-edge π* and σ* transitions. Experimental XANES spectra show that π* resonance increases with the incidence angle from normal to grazing incidence angle while σ* resonance decreases. This has been explained by the sine-square and cosine-square dependencies of π* and σ* intensities, respectively. These results were confirmed by theoretical XANES curves of highly oriented pyrolytic graphite (HOPG) and CNTs plotted versus incidence angle. It has been shown that π* and σ* transitions strongly depend on the nature of polarized light (linearly or circularly). At the linear polarized light, π* resonance is a preference as well as at right-circular polarized. At the left-circular polarized light, σ* resonance is a preference. The π* intensities are high at parallel orientation and the σ* intensities are low at normal orientation. The smallest π* intensity is noticed at normal orientation, where the π* orbitals are supposed to be lying parallel to the surface plane for perfectly aligned HOPG or CNTs. This explains the incomplete extinction of π* intensity. We noticed at parallel orientation a region where any π* and σ* transitions did not expect because of the lack of polarization light.

关键词： Angular Dependence XANES Normal Incidence Grazing Incidence Carbon Nanotubes Intensity

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Alignment of Vertically Grown Carbon Nanostructures Studied by X-Ray Absorption Spectroscopy

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Materials Sciences and Applications 2014年第13期5卷 966-983页

作者： Jeannot Mane Mane Francois Le Normand Rolant Eba Medjo Costel Sorin Cojocaru Ovidiu Ersen Antoine Senger Carine Laffon Bridinette Thiodjio Sendja César Mbane Biouele Germain Hubert Ben-Bolie pierre owono ateba Philippe Parent IPCMS UMR 7504 CNRSStrasbourgFrance Ecole Nationale Supérieure Polytechnique(National Advanced School of Engineering) Department of Mathematics and Physical SciencesThe University of YaoundéIYaoundeCameroon Physics Department Faculty of ScienceUniversity of YaoundéIYaoundeCameroon Physics Department Faculty of ScienceUniversity of DoualaDoualaCameroon LURE UMR CNRSCentre Universitaire Paris SudOrsayFrance

X-Ray Absorption Spectroscopy (XAS) on the carbon K edge of carbon nanostructures (nanotubes, nanofibers, nanowalls) is reported here. They are grown on plain SiO2 (8 nm thick)/Si(100) substrates by a Plasma and Hot Filaments-enhanced Catalytic Chemical Vapor Deposition (PE HF CCVD) process. The morphology and the nature of these carbon nanostructures are characterized by SEM, TEM and Raman spectroscopy. According to conditions of catalyst preparation and DC HF CCVD process, carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon nanowalls (CNWs), carbon nanoparticles (CNPs) with different orientation of the graphene plans or shells can be prepared. From the angular dependence of the incident light and geometrical morphology of the nanostructures, wide variations of the C K-edge intensity of the transitions to the empty π* and σ* states occur. A full lineshape analysis of the XAS spectra has been carried out using a home-made software, allowing estimating the relative proportion of π* and σ* transitions. A geometrical model of the angular dependence with the incidence angle of the light and the morphology of the carbon nanostructures is derived. With normalization to the HOPG (Highly Oriented Pyrolytic Graphite graphite) reference case, a degree of alignment can be extracted which is representative of the localized orientation of the graphitic carbon π bonds, accounting not only for the overall orientation, but also for local defects like impurities incorporation, structural defects ... This degree of alignment shows good agreement with SEM observations. Thus CNTs films display degrees of alignment around 50%, depending on the occurrence of defects in the course of the growth, whereas no special alignment can be detected with CNFs and CNPs, and a weak one (about 20%) is detected on CNWs.

关键词： X-Ray Absorption Spectroscopy Carbon Nanostructures(CNTs,CNFs,CNWs,CNPs) Plasma-and Hot Filaments-Enhanced Catalytic Chemical Vapor Deposition Geometrical Model Angular Dependence

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A Review of the Advances Made in Improving the Durability of Welded Wood against Water in Light of the Results of African Tropical Woods Welding

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Journal of Renewable Materials 2023年第3期11卷 1077-1099页

作者： Jean Jalin Eyinga Biwôlé Achille Bernard Biwolé Antonio Pizzi Joseph Zobo Mfomo César Segovia Atangana ateba Evariste Fedoung Fongnzossie Sahbi Ouertani Xinyi Chen Bénoît Ndiwe DieudonnéAbessolo pierre-Jean Meausoone Laboratory of Forest Resources and Wood Valorization University of DoualaP.O.Box.2701DoualaCameroon Laboratory of Mechanics University of DoualaP.O.Box.2701DoualaCameroon CETELOR University of LorraineP.O.Box.21042EpinalFrance ENSTIB-LERMAB University of LorraineP.O.Box.21042EpinalFrance Laboratory of Energetics and Thermal and Mass Transfers El Manar University of TunisTunisTunisia

Wood plays a major role in the production of furniture and wooden ***,in this process,the massive use of adhesives and plural connectors remains a definite problem for health and the ***,wood welding is a breakthrough in this *** paper reviews the applications of wood welding in furniture and construction and then examines advances in improving the durability of welded wood against *** contribution also highlights the need to join African tropical woods using the rotational friction welding *** to our results,these woods present interesting chemical singularities,which could provide solutions to the water vulnerability of the welded ***,the use of such a joining method would first free the Cameroonian furniture industry from the chemical industry,secondly position it at the forefront of new eco-design trends and thirdly make it competitive with other countries in the Central African *** works enrich the long and rich bibliography on the technique of wood welding,which has long been conspicuous by its absence of tropical woods.

关键词： Wood welding tropical woods water vulnerability chemical singularities natural durability

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Study of the Relative Variations of the Thermal Properties and Crystallinity of Blends (PP/EPR)/Calcium Carbonate

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Modeling and Numerical Simulation of Material Science 2021年第1期11卷 19-33页

作者： pierre Marcel Anicet Noah Fabien Betene Ebanda Louis-Max Ayina Ohandja ateba Atangana Laboratory of Mechanics ENSET University of Douala Douala Cameroon Department of Mechanical Engineering ENSET University of Douala Douala Cameroon

The objective of this paper is to investigate the relative variations of the constants of the thermal properties and the degree of crystallinity of the mixtures (PP/EPR)/Calcium carbonates elaborated with the Micro Bivis. We have strengthened the basic copolymer PP/EPR of a low level (5%) by three calcium carbonates models socal312, socal322v, Winnofil spm. We then subjected the different mixtures obtained, two cycles of a thermal loading under differential scanning calorimetry DSC. We finally focused on the thermal properties of isotactic polypropylene (TfP, TcP, ΔHfP, ΔHcP) and we calculated the degree of crystallinity of the mixtures. Reducing the energy cost of implementing mixtures is one of the objectives of this work. We quantified the relative variations of the above properties with those of the base copolymer. It shows that at a low loading rate of calcium carbonate, there is a decrease in the enthalpies of crystallization during the second exothermic cycle, with values that can reach 5.53 J/gPP for the basic copolymer PP/EPR. During the second endothermic cycle, there is an overall increase in isotactic polypropylene melting temperature values for all the blends as well as for the basic copolymer PP/EPR. There is evidence that calcium carbonates are useful for lowering the melting energy of isotactic polypropylene, even at a low loading rate for the majority. The number of endothermic cycles accentuates this phenomenon which is linked to the presence in our composites, of a so-called confined amorphous phase.

关键词： DSC PP/EPR CaCO3 Crystallinity Micro Bivis

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Geochemical characterization of the metasedimentary rocks of the Yaounde Group within the southernmost North Equatorial tectonic belt:insights into geodynamic evolution

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Acta Geochimica 2023年第6期42卷 1017-1034页

作者： Simon pierre Mbola Ndzana Moise Christian Balla ateba Germain Marie Monespérance Mboudou Moussa Nsangou Ngapna Jean Paul Sep Nlongang Solange Ipan Moise Bessong Jean Bosco Olinga Joseph Mvondo Ondoa Sébastien Owona Paul Bilong Department of Earth Sciences Faculty of ScienceUniversity of YaoundéIP.O.Box:812Yaounde´Cameroon Institute for Geological and Mining Research P.O.Box:4110NlongkakYaounde´Cameroon Department of Earth Sciences Faculty of ScienceUniversity of DoualaP.O.Box:24157DoualaCameroon Department of Geology Faculty of ScienceThe University of BueaP.O.Box:67BueaCameroon

The Proterozoic metasedimentary rocks of the Yaounde Group on the northern edge of the Congo Shield in Central Africa were investigated to understand their provenance and depositional ***,geochemistry,and field evidence helped to subdivide the metasediments into paragneiss,mica schist,chlorite schist,and quartzite which were derived from greywacke,shale,quartz arenite,litharenite *** are immature with some mature samples,moderately weathered and reworked Neo-and Post-Archean *** earth element signatures(Chondrite Eu/Eu^(*)≤1),enrichment of light rare earth elements over the heavy ones,and the La/Sc ratio(>0.7)are compatible with those of the intermediate and felsic sources from the upper continental *** metasediments were deposited in the continental arc setting and have evolved during Proterozoic times according to the Wilson cycle to form the West Gondwana including NE Brazil.

关键词： West Gondwana North Equatorial orogenic belt Yaounde Group Neoproterozoic basin Geochemistry of metasedimentary rocks Geodynamic evolution

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Implementation and Evaluation of Certain Properties of a Polymer Matrix Composite Material Reinforced by Fibrous Residues of Saccharum officinarumin View of an Applicability Orientation

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Journal of Minerals and Materials Characterization and Engineering 2021年第2期9卷 206-225页

作者： Marie Josette Ndengue Merlin Zacharie Ayissi pierre Marcel Anicet Noah Fabien Betene Ebanda Atangana ateba Department of Mechanical Engineering ENSET University of Douala Douala Cameroon Laboratory of Mechanics University of Douala Douala Cameroon Laboratory of Energy Materials Modelisation and Method University of Douala Douala Cameroon National Higher Polytechnic School University of Douala Douala Cameroon

This study examines the implementation and characterization of a polymer matrix composite material reinforced by sugarcane residues. The aim of the study is to enhance the abundantly produced sugarcane bagasse in the form of residues in the processing plants of said sugar cane. The composite material developed takes into account the size parameters and mass load rate of the reinforcement, the variations of which are between 2.5 mm and 4 mm respectively for the first parameter and 10% to 25% for the second. The load on the test tube during the test has a random orientation. The composite is polyester matrix. The cold compression moulding technique was used in the production of the various samples. Physical properties such as the rate of water absorption and the density of the composite are assessed. The three-point bending tests are carried out with the aim of inducing Young’s modulus from the elaborate samples. Analysis of physical properties shows that water absorption increases with the rate of residue load. The average water absorption rate of bagasse fibres is estimated at 8% for the 2.5 mm fiber size and 12% for the 4 mm fiber size for all composites. Mechanical characterization by bending tests reveals a fragile behavior of the samples tested. Young’s modulus decreases when the load rate of fibrous residues increases regardless of the size of the fibers.

关键词： Composite Polymer Bagasse Young Modulus Saccharum officinarum

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Physico-Chemical and Thermal Characterization of a Lignocellulosic Fiber, Extracted from the Bast of Cola lepidotaStem

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Journal of Minerals and Materials Characterization and Engineering 2020年第5期8卷 377-392页

作者： Ndoumou Belinga Rémy Legrand Meva’a Lucien Ouagne pierre Betene Ebanda Fabien Noah pierre Marcel Atangana ateba Jean Laboratoire de Mécanique (LME) UFD SI Université de Douala Douala Cameroun Laboratoire d’Ingénierie Civile et Mécanique Université de Yaoundé I Yaoundé Cameroun Laboratoire Génie de Production (LGP) ENI de Tarbes Tarbes France

In this research work, fiber extracted from the bark of Cola lepidota (CL) plant, grown in the flora of Southern part of Cameroon, was investigated for composites reinforcement. The investigation was carried via evaluation of water absorption capacity, moisture content, real density, porosity, chemical composition, chemical structure and thermal behaviour. It was discovered that the new fiber has relatively low moisture content and water absorption capacity similar to those of other investigated natural fibers such as flax, sisal, coconut, hemp and jute. Its porosity was found appropriate for composite production and the fiber was found to be thermally stable up to 230°C, with maximum degradation temperature of 325°C. The main constituents of the fibre include cellulose, hemicellulose and lignin. In conclusion, based on the properties investigated, this fiber is considered suitable for composite manufacture.

关键词： Cola lepidota Fiber Thermal Stability Physico-Chemical Characteristics FTIR-ATR Liber Stem

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Oxidized palm oil impairs reproductive functions and architectures in female rats

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Asian pacific Journal of Reproduction 2023年第4期12卷 182-193页

作者： Wankeu-Nya Modeste Kengne Inès T ateba Benjamin S Bend Fortune E Djeumeni Ornela N HathoDominique T Ngadjui E Moundipa Paul F Massoma DieudonnéL Dongmo Alain B Watcho pierre Department of Animal Organisms Biology Faculty of ScienceUniversity of DoualaDoualaCameroon Department of Animal Production Faculty of Agronomy and Agricultural SciencesUniversity of DschangDschangCameroon Department of Biochemistry Faculty of ScienceUniversity of YaoundéIYaoundéCameroon Department of Animal Biology Faculty of ScienceUniversity of DschangDschangCameroon

Objective:To evaluate the effects of three oxidized palm oil diets(OPD)on female rat reproductive ***:Forty-four female Wistar rats presenting five consecutive and regular estrous cycles were divided into 4 *** rats were fed with:a standard diet,70%of standard diet+30%oxidized palm oil diet(OPD1),OPD1+5 g of boiled yolk egg(OPD2)and OPD1+10%sucrose(OPD3)for 125 days,*** the feeding period,morphometric,estrous cycle,sexual behavior,gestation,biochemical and histomorphometric parameters were ***:All OPDs significantly increased abdominal circumference,body mass index and Lee index coupled to an irregularity and lengthening of the estrous *** significantly decreased appetite and consumption behaviours,quantic pregnancy index,fertility rate,implantation sites and index,serum progesterone and high-density lipoprotein levels,increased pre-implantation losses,anti-implantation activities,serum estradiol,triglycerides,total and low-density lipoprotein-cholesterol levels,and impaired brain and ovaries oxidative *** examinations revealed increases in the number of atresic and primary follicles and decreases in secondary,tertiary,Degraaf,total and corpus luteum follicles in ovaries coupled to a neurodegeneration of hypothalamic anteroventral periventricular neurons in the OPD groups compared to the standard diet ***:The three OPDs induce obesity and impair the female reproductive function,especially OPD2 and *** findings contribute to a better understanding of the adverse effects of palm oil bleaching on the reproductive function in female rats,which could be useful in the management of women with obesity-related sexual dysfunction.

关键词： Bleached palm oil Reproductive function Anteroventral periventricular nucleus Ovary Estrogen Progesterone Female rat

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Physico-Chemical and Thermal Characterization of Some Lignocellulosic Fibres: Ananas comosus(AC), Neuropeltis acuminatas(NA) and Rhecktophyllum camerunense(RC)

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Journal of Minerals and Materials Characterization and Engineering 2020年第4期8卷 205-222页

作者： Achille Désiré Omgba Betene Fabien Ebanda Betene Florian Martoïa pierre J. J. Dumont ateba Atangana pierre Marcel Anicet Noah Department of Mechanical Engineering ENSET University of Douala Douala Cameroon Laboratory of Mechanics University of Douala Douala Cameroon University of Lyon INSA-Lyon CNRS UMR5259 LaMCoS Lyon France

This paper focuses on the study of the physical, biochemical, structural, and thermal properties of plant fibres of Rhecktophyllum camerunense (RC), Neuropeltis acuminatas (NA) and Ananas comosus (AC) from the equatorial region of Cameroon. The traditional use of these fibres inspired researchers to investigated their properties. This study aims at improving the state of knowledge with a view to diversifying applications. The fibres are extracted by retting. Then, their apparent density was measured following the ASTM D792 standard and their water moisture absorption and moisture content were also evaluated. Their molecular structure was studied by ATR-FTIR spectroscopy. A quantitative analysis of the biochemical composition was performed according to the analytical technique for the pulp and paper industry (TAPPI). A TGA/DSC analysis was also performed. The results reveal that the AC, NA and RC fibres have densities of 1.26 ± 1.06, 0.846 ± 0.13 and 0.757 ± 0.08 g·cm-3 respectively. They are also hydrophilic with a water absorption rate of 188.64 ± 11.94%, 276.16% ± 8.07% and 198.17% ± 20%. They have a moisture content of 12.21%, 10.36% and 9.37%. The studied fibres exhibit functional groups that are related to the presence of hemicellulose, pectin, lignin and cellulose. The cellulose crystallinity index was found to be 67.99%, 46.5% and 59.72% respectively. The fibres under study have the following chemical composition: an extractive content of 3.07%, 14.77% and 8.74%;a pectin content of 4.15%, 7.69% and 3.45%;a hemicellulose content of 4.90%, 15.33% and 7.42%;a cellulose content of 68.11%, 36.08% and 65.15%;a lignin content of 12.01%, 25.15% and 16.2%;and an ash content of 0.27%, 1.53% and 0.47% respectively. The thermal transitions observed on the thermograms correlate with the TAPPI chemical composition. It is observed that these fibres are thermally stable up to temperatures of 200°C, 220°C and 285°C. These results ma

关键词： Lignocellulosic Fibre Rhecktophyllum camerunense Neuropeltis acuminatas Ananas comosus Biochemical Composition Cellulose Crystallinity Index Thermal Behaviour

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Elaboration and Characterization of a Hybrid Composite Material with Two Particles of the Same Size: Coco Shells and Palm Shells

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Open Journal of Composite Materials 2020年第4期10卷 77-91页

作者： pierre Marcel Anicet Noah Ebanda Fabien Betene Suzie Viviane Obame Beassoum Allasra Martin Christian Bindjeme ateba Atangana Laboratory of Mechanics ENSET University of Douala Douala Cameroon Department of Mechanical Engineering ENSET University of Douala Douala Cameroon

This work aims to develop and characterize a hybrid composite material with two particles of the same size. As reinforcing particles, the hulls of palm nuts and coconut are chosen. Hybrid composite material composites in the form of specimens were produced by molding at 10%, 20% and 30% mass fractions in various sizes (0.63 mm, 1.25 mm and 2.5 mm). The samples were physically characterized (water absorption rate, moisture content, actual, theoretical and apparent density) and mechanical in 3-point flexion. The main results are: the highest and minimum water absorption rate are respectively 3.57% and 0.67% for respectively particle sizes 1.25 mm (sample P10C30) and 0.67% in the size of 0.63 mm (sample P10C10). The moisture content varies from 0.64 to 7.14% respectively for the P20C20 (2.5 mm) and P10C30 (2.5 mm) samples. The maximum and minimum real density are 1340,518 Kg/m3 and 1055.981 Kg/m3, for respectively the composites of particles sizes 1.25 mm (P20C10) and 0.63

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