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Journal of Minerals and Materials Characterization and Engineering 2024年第5期12卷 265-279页

作者： Philémon Zo’o Zame Sylvain Kouayep Lawou Philippe Samba Assomo Audrey Erman Moutsou Yannick Lontchi Dzoti Véronique Kamgang Kabeyene Beyala Faculty of Science University of Yaound I Yaound Cameroon higher teacher training college bertoua University of Bertoua Bertoua Cameroon Faculty of Science University of Dschang Dschang Cameroon

The Mbouda alluvial deposit is located at the foot of the Bamboutos mountains (West Cameroon) where three types of clayey materials are widespread. The populations collect these clays in their natural state in view of constructions using fired bricks or compressed blocks. Unfortunately, these buildings are not strong. This study investigates the causes of the strengthlessness of buildings and suggests solutions to overcome the difficulty. The research content includes field and laboratory studies. The methodology consists of sampling black (AN), white (AB) and red (AR) clays specimens identified in the study area and analysing them simultaneously at MIPROMALO (Cameroon) and at ACME LAB in Vancouver (Canada). The results obtained show a high sand content in the samples AN (64%), AB (55.2%), AR (30.9%). The compressive strength of the built specimens is low at 900˚C considered as the traditional firing temperature AN (0.94 MPa), AB (5.25 MPa), AR (2.18 MPa). The mineralogical series are identically made by kaolinite, chlorite, gibbsite, quartz, muscovite, biotite, goethite, magnetite and hematite. Silica (SiO2) presents higher contents AN (52.87%), AB (48.02%), AR (47.68%) followed by alumina (Al2O3) AN (29.96%), AB (28.13%), AR (24.72%). The other elements are poorly represented.

关键词： Sand Bricks Clays Mechanical Properties Local Constructions

Multiscale Analysis of Semilinear Damped Stochastic Wave Equations

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Acta Mathematica Sinica,English Series 2023年第7期39卷 1305-1331页

作者： Aurelien FOUETIO Gabriel NGUETSENG Jean Louis WOUKENG Department of Mathematics Higher Teacher Training CollegeUniversity of NgaoundereP.O.Box 652BertouaCameroon Department of Mathematics University of Yaounde IP.O.Box 812YaoundeCameroon Department of Mathematics and Computer Science University of DschangP.O.Box 67DschangCameroon

In this paper we proceed with the multiscale analysis of semilinear damped stochastic wave motions. The analysis is made by combining the well-known sigma convergence method with its stochastic counterpart, associated to some compactness results such as the Prokhorov and Skorokhod theorems. We derive the equivalent model, which is of the same type as the micro-model. One of the novelties of the work is that the corrector problem is solved in the classical sense of distributions,thereby allowing numerical computations of the homogenized coefficients.

关键词： Hyperbolic stochastic equations Wiener Process sigma convergence tightness of probability measures

A Novel Hybrid MPPT for Wind Energy Conversion Systems Operating under Low Variations in Wind Speed

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Energy and Power Engineering 2020年第12期12卷 716-728页

作者： Paul Abena Malobe Philippe Djondine Pascal Ntsama Eloundou Hervé Abena Ndongo Department of Physics Faculty of Science The University of Ngaoundéré Ngaoundéré Cameroon Department of Physics Higher Teacher Training College of Bertoua The University of Ngaoundéré Bertoua Cameroon

This manuscript presents a new approach MPPT (Maximum Power Point Tracking) for improving and optimizing the performance of a Wind Energy Conversion System (WECS) operating for small variations in wind speed by combining sliding mode control and fuzzy logic control. The proposed method consists of optimizing the sliding mode controller by the fuzzy controller. The main purpose of the Sliding Mode control-Fuzzy Logic controller (SM-FL) is to ensure the robustness (by eliminating certain disadvantages of the sliding mode control such as the phenomenon of chattering) and the stability of the control system in the case of small variations in conditions atmospheric (here variation of the wind). Our system consists of a wind turbine, a Permanent Magnet Synchronous Generator (PMSG) and a DC-DC boost converter connected to a continuous load. The performances of the method suggested are compared with those of fuzzy logic and fuzzy-Proportional Integral (FL-PI) in term speed of convergence, of tracking time and tracking efficiency. The results of numerical simulation of our system confirmed the best performance of this method.

关键词： MPPT Sliding Mode-Fuzzy Logic Controller Wind Energy Conversion System Chattering

Quasi-Local Energy Distribution and Thermodynamics of Reissner-Nordstrom Black Hole Surrounded by Quintessence

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Communications in Theoretical Physics 2011年第2期55卷 291-295页

作者： Mahamat Saleh Bouetou Bouetou Thomas Timoleon Crepin Kofane Department of Physics Faculty of Science University of Yaounde Dpartment of Physics Higher Teacher's Training College University of Maroua Ecole Nationale Superieure Polytechnique University of Yaounde

We investigate quasi-local energy distribution and thermodynamics of the Reissner-Nordstr6m black hole space-time surrounded by quintessence. We use the quasi-local energy distribution from Einstein energy-momentum complex. We plot the variation of the energies, temperature and heat capacity with the state parameter related to the quintessence ωq. We show that due to the presence of quintessence, the total energy of the outer region as well as the temperature and heat capacity decreases with the increase of the density of quintessence, while the total energy of the black hole region increases.

关键词： quasi-local energy distribution thermodynamics Reissner-NordstrSm black hole quintessence

Travelling Wave Solutions to Stretched Beam's Equation: Phase Portraits Survey

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Communications in Theoretical Physics 2011年第4期55卷 605-608页

作者： Gambo Betchewe Kuetche Kamgang Victor Bouetou Bouetou Thomas Timoleon Crepin Kofane higher teacher's training college of Maroua University of Maroua Ecole Nationale Superieure Polytechnique University of Yaounde I Department of Physics Faculty of ScienceUniversity of Yaounde I

In this paper, following the phase portraits analysis, we investigate the integrability of a system which physically describes the transverse oscillation of an elastic beam under end-thrust. As a result, we find that this system actually comprises two families of travelling waves： the sub- and super-sonic periodic waves of positive- and negative- definite velocities, respectively, and the localized sub-sonic loop-shaped waves of positive-definite velocity. Expressing the energy-like of this system while depicting its phase portrait dynamics, we show that these multivaiued localized travelling waves appear as the boundary solutions to which the periodic travelling waves tend asymptotically

关键词： phase portraits elastic beam travelling waves

Removal of Dyes in Aqueous Media with Hydrochar Base of Solid Tanneries Waste: Optimization Process and Application

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Materials Sciences and Applications 2024年第7期15卷 168-185页

作者： Abdoul Ntieche Rahman Gervais Ndongo Kounou Sakué Ngankam Eric Tamafo Fouegue Aymard Didier Kouotou Daouda Abdelaziz Baçaoui Department of Chemistry Higher Teacher Training College Bertoua The University of Bertoua Bertoua Cameroon Department of Fundamental Sciences Institute of Wood Technology of Mbalmayo University of Yaound I Balmayo Cameroon Department of Chemistry Faculty of Science Semlalia University of Cady Ayyad Marrakech Morocco

The Response Surface Methodology (RSM) was used to optimise the conditions of preparation of activated hydrochar from tannery solid waste by hydrothermal carbonisation (HTC). The main factors such as residence time, moisture content and final carbonisation temperature were investigated during the optimisation of hydrochar preparation conditions. The three responses investigated are hydrochar yield, iodine and methylene blue indices. The results of experimental analyses showed that the yield of hydrochar decreases with increasing final temperature, leading to the formation of micropores inside the carbonaceous solid. The optimum conditions for preparing the following hydrochar were obtained: 83.10%, 390.44 mg∙g−1 and 259.63 mg∙g−1 respectively for the hydrochar yield, the iodine and methylene blue indices. The specific surface area of prepared hydrochar is 849.160 m2/g, SEM micrographs showed a porous heterogeneous surface and particularly, the hydrochar surface also revealed external pores on the hydrochar surface which acted as a pathway to the micropores. Fourier transform infrared (FTIR), however, showed a predominance of acid functions on the surface of the carbonaceous solids. Tests were carried out to eliminate indigo carmine in aqueous media. Activated hydrochar showed a high level of activity, with the Langmuir and Freundlich isotherms giving an adsorption quantity of 354.610 mol/g and a KF constant of 468.2489, respectively. The findings of the research revealed that hydrochar produced is well adapted for dyes removal.

关键词： Response Surface Methodology Hydrochar Tannery Hydrothermal Carbonization Adsorption

Assessment of Groundwater Quality for Domestic and Irrigation Purposes in Northern Bamenda (Cameroon)

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Journal of Water Resource and Protection 2021年第1期13卷 1-19页

作者： Alice Magha Margaret Tita Awah Gus Djibril Kouankap Nono Primus Azinwi Tamfuh Pierre Wotchoko Mercy Adoh Veronique Beyala Kamgang Kabeyene Department of Geology Higher Teacher Training College University of Bamenda Bambili Cameroon Department of Biology Higher Teacher Training College University of Bamenda Bambili Cameroon Department of Soil Science Faculty of Agronomy and Agricultural Sciences University of Dschang Dschang Cameroon Department of Mining and Mineral Engineering National Higher Polytechnic Institute University of Bamenda Bambili Cameroon Department of Earth Sciences Higher Teacher Training College University of Ngaoundere Bertoua Cameroon

Safe and reliable drinking water availability constitutes a nightmare in many towns of developing countries and is usually appreciated from its physical appearance without prior knowledge of its chemical and biological properties. This study investigates the suitability of groundwater for domestic and irrigational purposes through physico-chemical and bacteriological analyses in the Northern part of Bamenda Town (Cameroon). Thus, 20 groundwater samples were collected from hand-dug wells and spring sources in September 2018 (rainy season) and February 2019 (dry season) and physico-chemical and bacteriological characteristics were determined. The results revealed that pH ranged from 5.5 to 6.6, thus enabling the classification of the water as slightly acidic. Electrical conductivity varied between 0.01 - 0.06 μS/cm. The relative abundance of ions was such that Ca2+ > K+ > Mg2+ > Na+ for cations and HCO-3 > Cl- > NO-3 > SO-4 for anions. The water types were Ca-Mg-NO3 in both dry and rainy seasons. The results revealed that the mechanisms controlling groundwater chemistry are rock weathering and atmospheric precipitation. Indicator bacteria such as E. coli, Shigella, Enterobacteria, Vibrio, Streptococcus and Staphylococcus were detected in the studied groundwater samples, thus the water sources may pose a threat to public health.

关键词： Reliable Drinking Water Groundwater Quality Spring Sources Chemical Characteristics Bacteriological Characteristics

Generation of Hyperchaos from the LüSystem with a Sinusoidal Perturbation

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Journal of Applied Mathematics and Physics 2021年第5期9卷 1100-1107页

作者： Philippe Djondiné Paul Abena Malobé Department of Physics Higher Teacher Training College The University of Ngaoundéré Bertoua Cameroon Department of Physics Faculty of Sciences The University of Ngaoundéré Ngaoundéré Cameroon

This paper introduces a hyperchaotic system from the Lü system with a sinusoïdal perturbation. This hyperchaotic system has more complex dynamical behaviors, and can generate 2-scroll hyperchaotic attractor and 2-scroll chaotic attractor under different control parameters. Theoretical analyses and simulation are conducted to investigate the dynamical behaviors of the proposed hyperchaotic system by means of Lyapunov exponents, analysis of the bifurcation diagram and phase portraits.

关键词： Hyper-Chaotic Bifurcation Lü System Lyapunov Exponent

Mineralogy and geochemistry of sands of the lower course of the Sanaga River, Cameroon: implications for weathering,provenance, and tectonic setting

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Acta Geochimica 2021年第3期40卷 348-365页

作者： Marie Therese Nanga Bineli Vincent Laurent Onana Sylvie Desiree Noa Tang Yves Robert Bikoy Georges Emmanuel Ekodeck Department of Earth Sciences Faculty of ScienceUniversity of Yaounde IP.O.Box 812YaoundeCameroon Department of Geology Higher Teacher’s Training CollegeThe University of Yaounde IP.O.Box 47YaoundeCameroon

This study focuses on the mineralogy and bulk chemical composition of 19 sediment samples,collected from the Sanaga River bed,between Nanga-Eboko and the Atlantic Ocean in Cameroon,to infer provenance,weathering,and tectonic *** textural analysis revealed that these sediments are mainly coarse-grained sands.X-ray diffraction and heavy mineral analyses show that these sands are made of quartz,microcline,plagioclase,muscovite,ilmenite,anatase,magnetite,opaques,and *** Index of Chemical Variability values(1.07–2.68)indicates that the sands are *** Chemical Index of Alteration(53–66%),Plagioclase Index of Alteration(PIA;57–75%),and Mafic Index of Alteration(54–67%)values revealed a moderate intensity of weathering for these *** to the compositional maturity diagram,the sands are mainly *** studied sands show enrichment in light rare earth elements relative to heavy rare earth elements and a negative anomaly in Eu(Eu/Eu*=0.32–0.83).These sands were derived from felsic metamorphic rocks dated Meso to Neoproterozoic from the Pan-African(700–1000 Ma)domain of south ***/U ratios(mean=5.40;n=19)reveal that these sands originating from felsic source rocks and are low to moderately *** the tectonic discrimination diagrams,all the samples are plotted in the rift and passive margin domains,which is consistent with the tectonic history of Pan African in southern Cameroon.

关键词： Central Africa Sanaga River sediments Heavy minerals Major and trace elements Source rocks Rift and passive setting

Investigation of the Antioxidant and UV Absorption Properties of 2-(2’-hydroxy-5’-methylphenyl)-benzotriazole and Its Ortho-Substituted Derivatives via DFT/TD-DFT

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Computational Chemistry 2021年第3期9卷 161-196页

作者： Numbonui Stanley Tasheh Aymard Didier Tamafo Fouegue Julius Numbonui Ghogomu Research Unit of Noxious Chemistry and Environmental Engineering Department of Chemistry Faculty of Science University of Dschang Dschang Cameroon Department of Chemistry Higher Teacher Training College Bertoua University of Ngaoundéré Bertoua Cameroon Department of Chemistry Faculty of Science The University of Bamenda Bamenda Cameroon

The demand and pursuit of chemical entities with UV filtration and antioxidant properties for enhanced photoprotection have been driven in recent times by acute exposure of humans to solar ultraviolet radiations. The structural, electronic, antioxidant and UV absorption properties of drometrizole (PBT) and designed ortho-substituted derivatives are reported via DFT and TD-DFT in the gas and aqueous phases. DFT and TD-DFT computations were performed at the M062x-D3Zero/6-311++G(d,p)//B97-3c and PBE0-D3(BJ)/def2-TZVP levels of theory respectively. Reaction enthalpies related to hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) mechanisms were computed and compared with those of phenol. Results show that the presence of -NH2 substituent reduces the O-H bond dissociation enthalpy and ionization potential, while that of -CN increases the proton affinity. The HAT and SPLET mechanisms are the most plausible in the gas and aqueous phases respectively. The molecule with the -NH2 substituent (PBT1) was identified to be the compound with the highest antioxidant activity. The UV spectra of the studied compounds are characterized by two bands in the 280 - 400 nm regions. Results from this study provide a better comprehension antioxidant mechanism of drometrizole and present a new perspective for the design of electron-donor antioxidant molecules with enhanced antioxidant-photoprotective efficiencies for applications in commercial sunscreens.

关键词： Antioxidant Drometrizole Density Functional Theory Ultraviolet Absorption Hydrogen Atom Transfer Single Electron-Proton Transfer and Sequential Proton Loss Electron Transfer Mechanisms