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Microstructure and Oxidation Protection Behavior of Mullite/SiC Coating on C/C Composites

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Microstructure and Oxidation Protection Behavior of Mullite/...

作者： Gbologah,lemuel（李木）中南大学

学位级别：硕士

炭/炭复合材料在高温具有优异的机械性能,广泛的应用于航空航天领域。尽管如此,在高于500℃且无氧化保护的情况下,炭／炭复合材料极易受氧化和挥发的影响。为了改善其高温抗氧化性,相匹配的氧扩散屏障被重视和发展。针对这一问题,采用... 详细信息

炭/炭复合材料在高温具有优异的机械性能,广泛的应用于航空航天领域。尽管如此,在高于500℃且无氧化保护的情况下,炭／炭复合材料极易受氧化和挥发的影响。为了改善其高温抗氧化性,相匹配的氧扩散屏障被重视和发展。针对这一问题,采用了氧化铝成分含量72-84 wt.%的莫来石和碳化硅反应层的双层涂层,涂覆于炭/炭复合材料上。通过两步涂层法：1800℃的包埋烧结法和550℃的涂覆涂层法。采用软木粉做为包埋法制备碳化硅涂层的脱模剂,商业熔凝莫来石做为一种参考材料引入。涂层后样品的性能通过高温1500℃、空气气氛中的循环氧化实验进行评价,循环周期数为10个。通过XRD、SEM对样品的物相和结构进行表征,结果表明,炭/炭复合材料的双层(莫来石一碳化硅层)可以通过低成本的包埋烧结法和涂覆涂层法制得,基体密度对涂层性能具有重要的影响。高密度基体可获得致密且具有一定厚度的涂层。涂覆了商业莫来石的低密度炭/炭复合材料在106h的氧化实验后,质量减少。相比之下,高密度的基体制备的涂层样品,在氧化实验后的的质量增加。部分原因为,碳化硅渐变层和高温时在样品表层形成的氧化产物一二氧化硅层使自身微裂纹自动愈合的商业莫来石一硅胶涂覆涂层发挥了作用。1500℃高温氧化106h后,在高密度基体上获得的商业莫来石抗氧化层比低密度基体的涂层能更有效地对基体进行保护。高密度样品的增重率为约5.17%即1.4 gcm-2h-1;低密度样品的失重率为约50.34%即12.8gcm-2h-1。尽管如此,溶胶凝胶合成的氧化铝成分为84、79、76和72wt.%莫来石,在110h的高温氧化实验之后仍附着于β-SiC-C/C基体上,且与只有13.2μm厚的碳化硅涂层相比,商业莫来石一碳化硅涂层中205.9μm的碳化硅涂层并没有扩散到基体中。氧化铝含量较高的溶胶凝胶合成莫来石具有最优化的抗氧化能力。氧化铝含量为84 wt.%的溶胶凝胶合成莫来石涂层样品的的失重率为0.09 gcm-2h-1;相比之下,氧化铝含量为72 wt.%的溶胶凝胶合成莫来石涂层样品的失重率为0.20gcm-2h-1。

关键词：炭/炭复合材料溶胶凝胶莫来石包埋法涂敷涂层法氧化

Systematically controlled synthesis of rGO/nano-MnOx materials for supercapacitors

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Progress in Natural Science:Materials International 2019年第5期29卷 504-510页

作者： Xiaoyu Zhao Haocun Yang Yongdan Hou lemuel Gbologah Liang Zhu Yanfei Wang Tianjin Key Laboratory of Marine Resources and Chemistry College of Chemical Engineering and Materials Science Tianjin University of Science and Technology College of Engineering Kwame Nkrumah University of Science and Technology College of Art and Built Environment Kwame Nkrumah University of Science and Technology College of Chemical Engineering and Materials Science Tianjin University of Science and Technology

The effects of hydrothermal production conditions on crystal forms,morphology and electrochemical performance of in situ reduced graphene oxide/manganese oxides（r GO/Mn Ox）hybrid electrode materials were *** XRD/SEM results show that the ratio of precursors,reaction temperature and type of solvent significantly affected the crystal form obtained and nano-structure of *** precursor ratios of KMnO4:GO（5:1,7:1,9:1 and 11:1）yielded the hybrids of rGO/Mn7O135H2O,rGO/β-MnO2,rGO/Mn98O2,and rGO/K0.27MnO2（H2O）0.54,respectively,having corresponding nano structures of nano-sheets composed petal-like shape,petal-like shape based nano-wire clusters,petal-like shape with backwardly arched top and bigger mesoporous petal-like nano *** prepared precursor with the ratio of 5:1 exhibited the highest specific capacitance of 320 F/g at 0.2 A/g and the smallest diffusion ***,hybrid prepared precursor with the ratio of 7:1 presented the lowest electron transfer *** hydrothermal treatment temperatures（140,160 and 200℃）yielded hybrids:rGO/MnO（OH）,rGO/Mn0.91O1,82（H2O）0.18,and rGO/Mn7O135H2O,*** nano structures of the hybrids were nano-sheets having petal-like mesoporous structure,but having larger dimensions as temperature *** hybrid prepared at 160℃ showed the highest specific capacitance of 214 F/g at a current density of 0.2 A/g and the lowest solution resistance of1.61Ω,whiles,the hybrid prepared at 140℃ inferred the best cyclic reversibility.

关键词： Manganese oxides Crystal structure Hydrothermal treatment Specific capacitance Supercapacitors

Preparation and oxidation property of ZrB_2-MoSi_2/SiC coating on carbon/carbon composites

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Transactions of Nonferrous Metals Society of China 2011年第7期21卷 1538-1544页

作者：张武装曾毅 GBOLOGAH lemuel 熊翔黄伯云中南大学粉末冶金国家重点实验室长沙410083

To improve the oxidation resistance of carbon/carbon composites,ZrB2-MoSi2/SiC coating on the carbon/carbon substrate was *** inner coating of SiC was prepared by pack cementation and the outer coating of ZrB2-MoSi2 was prepared by slurry *** phase compositions and microstructures of the coating were characterized by XRD and SEM,*** preparation and the high temperature oxidation property of the coated composites were *** results show that the outer coating of carbon/carbon composites is composed of ZrB2,MoSi2 and SiC *** mass losses of the ZrB2-MoSi2/SiC coated samples with SiC nano-whiskers after 30 h and 10 h of oxidation at 1 273 K and 1 773 K were,respectively,5.3% and 3.0%.The ZrB2-MoSi2/SiC coated samples exhibit self-sealing performance and good oxidation resistance at high temperature.

关键词： carbon/carbon composites ZrB2-MoSi2 SiC coating oxidation

Pressure-Dependent Models in Ship Piping Systems

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Journal of Marine Science and Application 2020年第2期19卷 266-274页

作者： Daniel Molina Pérez lemuel C.Ramos-Arzola Amadelis Quesada Torres Departamento de Manufactura ESIME Unidad AzcapotzalcoInstituto Politécnico NacionalDF 02250 México CityMexico Departamento de Termofluidos ESIME Unidad AzcapotzalcoInstituto Politécnico NacionalDF 02250 México CityMexico

This paper aims to evaluate the feasibility of pressure-dependent models in the design of ship piping *** this purpose,a complex ship piping system is designed to operate in firefighting and bilge services through jet *** system is solved as pressure-dependent model by the piping system analysis software EPANET and by a mathematical approach involving a piping network *** results in a functional system that guarantees the recommendable ranges of hydraulic state variables(flow and pressure)and compliance with the rules of ship classification *** this research,the suitability and viability of pressure-dependent models in the simulation of a ship piping system are proven.

关键词： Pressure-dependent models Ship piping systems Bilge systems Firefighting systems Piping network models

Genotypic Variation in Yield and Yield Components of Plantain (<I>Musa</I>spp.) in Response to Containerized Planting Material and Mulching

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Agricultural Sciences 2018年第4期9卷 416-425页

作者： lemuel Ohemeng Mintah Godfred Kwabena Ofosu-Budu Nana Oduro Osei-Bonsu Forest and Horticultural Crops Research Centre Kade School of Agriculture College of Basic and Applied Sciences University of Ghana Legon Ghana

The study was conducted to evaluate the field performance of local plantain genotypes;Apem, Oniaba, Apantu (AAB) and FHIA 21 (AAAB) suckers that were raised in containers (polybags) and their corresponding conventional suckers. Half of the containerized and conventional suckers in each plot were mulched with empty fruit bunch (EFB). Survival rate three months after transplanting was higher in containerized (100%) than conventional materials (60%) with or without mulching. Mulching increased the girth at flowering and total leaf area by 8% and 28% respectively, and reduced the number of days to flowering. Mulching also increased yield of plantain and the highest was recorded in FHIA 21. Bunch yield of container raised suckers per hectare was 19% greater than conventional suckers, due to higher survival rate after transplanting. Bunch yield among the genotypes in decreasing order was as follows, FHIA21 (20.7), Oniaba (16.9), Apem (15.9) and Apantu (13.2) tons/ha. Mulching increased the yield components such as, pulp weight, peel weight, finger weight and number of fingers. Genotypic variation in pulp yield was in the following decreasing order Apantu > FHIA 21 > Oniaba > Apem fresh weight. The pulp to peel ratio was in the following decreasing order Apantu > FHIA 21 > Apem > Oniaba. It is concluded that raising plantain suckers in polybags and applying EFB mulch is an improved production technique.

关键词： Containerized Planting Material Conventional Planting Material Plantain Genotypes Mulching

Prenatal and Postnatal Exposures to 1-Methyl-4-phenyl-1,2,3,6-tetra Hydropyridine (MPTP) Impaired Mouse Midbrain Dopamine System and May Produce a Predisposing and Inducing Model for Parkinson’s Disease

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Journal of Behavioral and Brain Science 2012年第4期2卷 485-494页

作者： Gladson Muthian Jennifer King lemuel Dent Marquitta Smith Veronica Mackey Clivel Charlton Department of Neuroscience and Pharmacology Meharry Medical College Nashville USA

Dopamine cell bodies in the substantia nigra of the midbrain and with their terminals projecting to the neostriatum form the nigrostriatum and these dopamine neurons degenerate in Parkinson’s disease (PD). Based on metabolic and func- tional specialization of the cell bodies versus the axon terminals, the level and disposition of dopamine, its metabolites and enzymes are different in both regions and are likely to be affected differently in PD. We examined changes in the midbrain dopamine system following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), to test the hypothesis that a predisposing/sensitization stage and a inducing/precipitating stage underlie PD. Pregnant mice were treated with a low dose of MPTP during gestation days 8 - 12 to model the predisposing/sensitization stage, by interrupting the fetal mid- brain dopamine system during its neurogenesis. For the inducing/precipitating stage, the 12-weeks offspring were ad- ministered MPTP. The prenatal-MPTP offspring appear normal, but midbrain dopamine, 3,4-di-hydroxy-phenyl-acetic- acid, 3-methoxytyramine, tyrosine-hydroxylase and L-aromatic-amino-acid-decarboxylase, were reduced by 49.6%, 48%, 54%, 20.9% and 25%. Postnatal-MPTP of 10, 20, 30 mg/kg administered to the prenatal-PBS vs prenatal-MPTP offspring reduced midbrain dopamine by 43.6%, 47.2%, 70.3% vs 85.4%, 89.1%, 95.2%;tyrosine-hydroxylase by 30%, 63%, 81% vs 30.7%, 70.4%, 91.4%;L-aromatic-amino-acid-decarboxylase by 0%, 2%, 40% vs 32%, 40%, 58%. The prenatal-MPTP may render the DA system sensitive by causing sub-threshold reduction of DA, its metabolites and en- zymes, enabling postnatal-MPTP to reduce dopamine above the 70% - 80% PD-inducing threshold. Thus, the study may produce a prenatal predisposing/sensitization and postnatal inducing/precipitation model of PD. It also indicates that some cases of PD may have a fetal basis, in which sub-threshold nigrostriatal impairments occur early in life and PD-symptoms are induced during aging by

关键词： Parkinson’s Disease Midbrain 1-Methyl-4-Phenyl-1 2 3 6-Tetrahydropyridine (MPTP) Dopamine Tyrosine Hydroxylase L-aromatic Amino Acid Decarboxylase Sensitization Precipitation

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可加速珊瑚礁生长恢复的水下混凝土构件项目

世界建筑导报 2010年第1期25卷 62-67页

作者： lemuel Alfeche Ronald Rodriguez

项目地点:菲律宾项目类型:环境工程开工日期:2006年元月该项目利用预先铸造的混凝土构件,使用增量基础设施改善海洋环境。

关键词：混凝土构件

Soft tissue sarcoma with metastasis to the stomach: A case report

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World Journal of Gastroenterology 2010年第40期16卷 5130-5134页

作者： lemuel Leon Dent Cesar Yamil Cardona Michael Clause Buchholz Roosevelt Peebles Julie Denise Scott Derrick Jerome Beech Billy Ray Ballard Department of Surgery Meharry Medical College Department of Gastroenterology Meharry Medical College Department of Plastic Surgery Meharry Medical College Department of Pathology Meharry Medical College

Soft tissue sarcomas are unusual malignancies comprising 1% of cancer diagnoses in the United States. Undifferentiated pleomorphic sarcoma accounts for approximately 5% of sarcomas occurring in adults. The most common site of metastasis is the lung, with other sites being bone, the brain, and the liver. Metastasis to the gastrointestinal tract has rarely been documented. We present an unusual case of high-grade pleomorphic sarcoma with metastasis to the stomach, complicated by upper gastrointestinal bleeding.

关键词： Gastrointestinal bleeding Metastatic sarcoma Undifferentiated pleomorphic sarcoma

Day of Surgery Cancellation in Urology at a Public Tertiary Hospital and a Private Specialist Hospital

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Open Journal of Urology 2017年第1期7卷 22-29页

作者： Mathew Yamoah Kyei James Edward Mensah lemuel Davies Bray Foli Ashiagbor Joseph Awuku-Asabre Bernard Toboh Department of Surgery and Urology School of Medicine and Dentistry College of Health Sciences University of Ghana Accra Ghana

Background: There is a high variability in the reasons for cancellation of elective urological surgery cases. Case cancellation rate is expected to be high in the Public Health System with perceived inefficiencies compared to private facilities in the same developing economy. Aims and Objectives: This comparative analysis was to determine the case cancellation rate and the reasons for cancellation of elective urological surgeries in a public tertiary hospital and a private specialist hospital in Accra. This is intended to form a basis for interventions aimed at reducing the case cancellation rate. Methods: This was a retrospective analysis of prospectively collected data on Day of Surgery cancelled elective urological cases from September 2014 to October 2015 at the urology unit of the Korle-Bu Teaching Hospital (KBTH), a public Tertiary Hospital and the Trust Specialist Hospital (TSH), a privately managed hospital in Accra. The reasons for case cancellation were categorized into structural factors, patient factors and process factors. Results: There was no significant difference between the case cancellation rate for elective urological cases at KBTH and the TSH which were 20.8% and 17.1% respectively (p = 0.317). For KBTH, the reasons for cancellation of elective urological cases were due to structural factors in 11/117 (9.4%), patient factors in 15/117 (12.8%) and process factors in 91/117 (77.8%) which was due mainly to surgery running late. At the TSH, the reasons were due to structural factors in 1/29 (3.4%), patient factors in 27/29 (93.1%) mainly due to patient not turning up and process factors in 1/29 (3.4%). Conclusion: The case cancellation rate of elective urological surgeries in both the Public Tertiary Hospital and the Private Specialist Hospital were high with no significant difference between the two. However, in the Public Tertiary Hospital, process factors predominated as the cause of these cancellations while patient factors were the predominant

关键词： Elective Urological Surgery Case Cancellation Public Tertiary Hospital Private Specialist Hospital