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Kinetics and Morphological Analysis of Silver Platinum Bimetallic Nanoparticles

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Acta Metallurgica Sinica(English Letters) 2016年第4期29卷 320-325页

作者： fredrick Okumu Mangaka Matoetoe Department of Chemistry Cape Peninsula University of Technology

Kinetics of a one-pot core-shell synthesis of bimetallic （BM） silver-platinum （Ag-Pt） nanoparticles （NPs） by simultaneous reduction of 1：1 mol fraction of precursors H2PtC16.6H20 and AgNO3 in aqueous solution is reported. Kinetics analysis was done by plotting UV-visible absorptions versus reaction time with a first-order fitting. Recorded constants of Ag NPs （0.079 s^-1）, Ag-Pt NPs 1：1 （0.082 s^-1）, and Pt NPs （0.006 s^-1） were obtained. The NPs suspension solutions were clear, free from AgCl precipitate, and had characteristic optical properties of 450 nm （Ag NPs）, while there were no observable bands for Pt and BM NPs. Morphological analysis using transmission electron microscopy, energy- dispersive X-ray spectroscopy （EDX）, and selected area electron diffraction （SAED） depicted spherical aggregates of Ag NPs, Pt NPs and core shell Pt-Ag NPs 1：1 of average size of 60, 2.5, and 20 mm, respectively. Presence of the Ag and Pt elemental composition in the nanoparticle suspensions was confirmed by EDX. SAED ring patterns revealed a single facecentered cubic crystalline nature of Ag NPs and showed typical Pt-based BMs randomly overlapped ring pattern with sharp diffraction spots.

关键词： Platinum Silver Bimetallic nanoparticles Kinetics Morphology

Effect of Bimodal Grain Size Distribution on the Strain Hardening Behavior of a Medium-Entropy Alloy

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Acta Metallurgica Sinica(English Letters) 2021年第4期34卷 465-475页

作者： Ibrahim Ondicho Bernard Alunda fredrick Madaraka Melody Chepkoech Department of Mechanical Engineering Dedan Kimathi University of TechnologyPrivate bag-10143Dedan KimathiNyeriKenya Materials Designand Manufacturing(MADEMA)GroupDedan Kimathi University of TechnologyPrivate Bag-10143Dedan KimathiNyeriKenya Department of Mining and Minerals Processing Engineering Taita Taveta UniversityP.O.Box 635-80300VoiKenya Department of Mechanical Engineering Howard University23006th Street NWWashingtonDCUSA

The evolution of strain hardening behavior of the Fe_(50)(CoCrMnNi)_(50) medium-entropy alloy as a function of the fraction of recrystallized microstructure and the grain size was studied using the Hollomon and Ludwigson *** specimens under study were partially recrystallized,fully recrystallized with ultrafine-grained microstructure,and fully recrystallized with coarse *** yield strength decreases steadily as the fraction of recry stallized micro structure and grain size increases due to the recovery process and the Hall-Petch ***,the bimodal grain distribution was found to have a significant impact on strain hardening during plastic *** instance,the highest ultimate tensile strength was exhibited by a 0.97 μm specimen,which was observed to contain a bimodal grain ***,using the Ludwigson equation,the effect of the bimodal grain distribution was established from the behavior of K_(2) and n_(1) *** curves tend to show very high values in the specimens with a bimodal grain distribution compared to those that show a homogenous grain ***,the bimodal grain distribution contributes to the extensive Luders strain observed in the 0.97 μm specimen,which induces a significant deviation of the Hollomon equation at lower strains.

关键词： Metals and alloy Mechanical properties Microstructure High-entropy alloys Plastic deformation

An Efficient Smoothing and Thresholding Image Segmentation Framework with Weighted Anisotropic-Isotropic Total Variation

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Communications on Applied Mathematics and Computation 2024年第2期6卷 1369-1405页

作者： Kevin Bui Yifei Lou fredrick Park Jack Xin Department of Mathematics University of CaliforniaIrvineIrvineCA 92697-3875USA Department of Mathematics University of North CarolinaChapel HillChapel HillNC 27599.USA Department of Mathematics and Computer Science Whittier CollegeWhittierCA 90602USA

In this paper,we design an efficient,multi-stage image segmentation framework that incorporates a weighted difference of anisotropic and isotropic total variation(AITV).The segmentation framework generally consists of two stages:smoothing and thresholding,thus referred to as smoothing-and-thresholding(SaT).In the first stage,a smoothed image is obtained by an AITV-regularized Mumford-Shah(MS)model,which can be solved efficiently by the alternating direction method of multipliers(ADMMs)with a closed-form solution of a proximal operator of the l_(1)-αl_(2) *** convergence of the ADMM algorithm is *** the second stage,we threshold the smoothed image by K-means clustering to obtain the final segmentation *** experiments demonstrate that the proposed segmentation framework is versatile for both grayscale and color images,effcient in producing high-quality segmentation results within a few seconds,and robust to input images that are corrupted with noise,blur,or *** compare the AITV method with its original convex TV and nonconvex TVP(O

关键词： Image segmentation Non-convex optimization Mumford-Shah(MS)model Alternating direction method of multipliers(ADMMs) Proximal operator

Bioprospecting optimal phenology for bioactive molecules in native golden yellow Pleurotus citrinopileatus Singer

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Asian Pacific Journal of Tropical Biomedicine 2016年第2期6卷 132-142页

作者： Godfrey Nattoh Erastus Gatebe fredrick Musieba Julius Mathara Department of Molecular Biology and Biotechnology Pan African University Institute for Basic SciencesTechnology and Innovation Research Technology and Innovation Department Kenya Industrial Research and Development Institute Department of Chemistry Jomo Kenyatta University of Agriculture Science and Technology Department of Food Science and Technology Jomo Kenyatta University of Agriculture Science and Technology

Objective: To bioprospect optimal phenological phases as source of novel molecules from native golden yellow Pleurotus citrinopileatus across four phenologies in both aqueous and ethanol extracts, and identify novel molecules responsible for these ***: Standard qualitative assay, Folin–Ciocalteu assay; aluminium chloride spectrophotometric, 2, 2-diphenyl-1-picrylhydrazyl, 2, 20-azinobis(3-ethylbenzothiazoline-6-suslfonic acid, ferricyanide reducing antioxidant power were used to determine total flavonoid, polyphenols, radical scavenging, and reducing power. Spectrophotometric methods were used for lycopene, b-carotene, and total carotenoids, while liquid chromatography quadrupole time of flight mass spectrometry was used for identification and comparative quantitation of polyphenols and flavonoids across the four phenological states. Chem Spider? database was used for the identification of compounds based on their empirical formula, accurate mass and literature review of previously reported compounds in ***: Primordial phases exhibited higher contents of secondary metabolites than mature basidiocarps. Polyphenols content differed across physiological phases with primordials exhibiting significant high contents(P < 0.05) [(13.803 ± 0.797) mg gallic acid equivalent/g dry weight]. Distribution of total flavonoids was significantly different(P < 0.05) across physiological states and ranged from(3.311 ± 0.730) to(14.824 ± 0.890) mg quercetin equivalent g dry weight. Ten polyphenol acids and seven flavonoids compounds identified varied across these phases with primordials exhibiting relatively high peak areas. Total antioxidant activities showed a positive correlation with total polyphenols(r = 0.969;P < 0.05) and total flavonoids(r = 0.960; P < 0.05) across these ***: These findings provide evidence that primordials of golden yellow mushroom as opposed to their fruiting bodies are potent sources of bioactive health molecule

关键词： Bioprospecting Primordial Phenology Bioactive molecules Liquid chromatography-quadrupole time of flight mass spectrometry Edible fungi

Comparative study of two modeling approaches for predicting heavy metals contaminant migration from polyethylene bags

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International Journal of Agricultural and Biological Engineering 2016年第3期9卷 194-200页

作者： Noble Banadda fredrick Lule Cornelius Sempala Julia Kigozi Department of Agricultural and Bio-Systems Engineering Makerere UniversityUganda Department of Educational Foundations and Curriculum Makerere UniversityUganda

Plasto-Foam brand,medium size of 30 mm thickness(black and green)commonly used polyethylene bags for preparing foods were selected from those available in local *** polyethylene bag samples were crushed into pieces,ashed and then acid digested to determine the concentrations of heavy metals selected(Pb,Cr,Co and Cd)using Atomic Absorption *** the polyethylene samples were tested positive for heavy *** of heavy metals in polyethylene bags ranged from 1080 ppm to 1725 ppm,76 ppm to 112 ppm,35 ppm to 52 ppm,18 ppm to 31 ppm for Pb,Cd,Cr and Co,***-eight posho(Ugali)samples were prepared and wrapped in these polyethylene bags and migration studies were carried out at 65°C and 80°*** experimental data obtained were then compared to the modeled data using the models developed by Baner et al.,and Limm and Hollifield to determine which model was a better *** fitting was done based on Non-linear least square analysis using Microsoft EXCEL *** and partition coefficients both between food and the contact material were also obtained by fitting experimental data to the model *** modeling approaching could best describe the experimental data of the measured *** study revealed that all polyethylene bags showed highest contaminant concentration(above USFDA limit)of Pb,Cd,Cr and Co,respectively confirming the potential health risk to individuals if continuously eat food thermally prepared in polyethylene bags.

关键词： heavy metals polyethylene bags migration mathematical models

DoS detections based on association rules and frequent itemsets

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Journal of Harbin Institute of Technology(New Series) 2008年第2期15卷 283-289页

作者： George S Oreku fredrick JMtenzi 李建中 Dept.of Computer Science and Engineering Harbin Institute of Technology School of Computing Dublin Institute of Technology

To detect the DoS in networks by applying association rules mining techniques, we propose that association rules and frequent itemsets can be employed to find DoS pattern in packet streams which describe traffic and user behaviors. The method extracts information from the log analysis of submitted packets using the algorithm which depends on the definition of the intrusion. Large itemsets were extracted to represent the super facts to build the association analysis for the intrusion. Network data files were analysed for experiments. The analysis and experimental results are encouraging with better performance as packet frequency number increases.

关键词： data mining intrusion packets streams

Hemolymph proteins in marine crustaceans

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Asian Pacific Journal of Tropical Biomedicine 2012年第6期2卷 496-502页

作者： W Sylvester fredrick S Ravichandran CAS in Marine Biology Faculty of Marine Sciences Annamalai University

This study is done with the aim to bring together the various antimicrobial peptides that are present in the crustacean hemolymph and their sources along with its *** lack immune systems that involve antigen-antibody reactions and do not have an immune memory, therefore most invertebrate species show no evidence of acquired *** possess an open circulatory system, where nutrients, oxygen, hormones, and cells are distributed in the hemolymph. They lack adaptive immune system and rely exclusively on their innate immune mechanisms that include both cellular and humoral responses. Antimicrobial peptides and proteins form an important means of host defense in eukaryotes. In addition to their role as endogenous antibiotics, antimicrobial peptides have functions in inflammation,wound repair and regulation of the adaptive immune system. Over the past several years, many antimicrobial peptides have been found and characterized in crabs.

关键词： Antimicrobial peptides Crabs Antibiotics Protein characterisation Immune response

Structure of the 40S ribosomal subunit of Plasmodium falciparum by homology and de novo modeling

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Acta Pharmaceutica Sinica B 2017年第1期7卷 97-105页

作者： Harrison Ndung'u Mwangi Peter Wagacha Peterson Mathenge fredrick Sijenyi Francis Mulaa Center for Biotechnology and Bioinformatics Chiromo CampusUniversity of Nairobi.HEP Bioinformatics Consultants Ltd. Department of Computing Informatics University of Nairobi DNA Software Inc. Department of Biochemistry Riverside DriveChiromo CampusUniversity of Nairobi

Generation of three dimensional structures of macromolecules using in silico structural modeling technologies such as homology and de novo modeling has improved dramatically and increased the speed by which tertiary structures of organisms can be generated. This is especially the case if a homologous crystal structure is already available. High-resolution structures can be rapidly created using only their sequence information as input, a process that has the potential to increase the speed of scientific discovery. In this study, homology modeling and structure prediction tools such as RNA123 and SWISS–MODEL were used to generate the 40 S ribosomal subunit from Plasmodium falciparum. This structure was modeled using the published crystal structure from Tetrahymena thermophila, a homologous eukaryote. In the absence of the Plasmodium falciparum 40 S ribosomal crystal structure, the model accurately depicts a global topology, secondary and tertiary connections, and gives an overall root mean square deviation(RMSD) value of 3.9 ? relative to the template's crystal structure. Deviations are somewhat larger in areas with no homology between the templates. These results demonstrate that this approach has the power to identify motifs of interest in RNA and identify potential drug targets for macromolecules whose crystal structures are unknown. The results also show the utility of RNA homology modeling software for structure determination and lay the groundwork for applying thisapproach to larger and more complex eukaryotic ribosomes and other RNA-protein complexes. Structures generated from this study can be used in in silico screening experiments and lead to the determination of structures for targets/hit complexes.

关键词： Ribosome 40S subunit RNA structure Plasmodium falciparum 3D modeling De novo Homology

Fate Processes of Chlorobenzenes in Soil and Potential Remediation Strategies: A Review

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Pedosphere 2017年第3期27卷 407-420页

作者： Ferdi BRAHUSHI fredrick Orori KENGARA SONG Yang JIANG Xin Jean Charles MUNCH WANG Fang Key Laboratory of Soil Environment and Pollution Remediation Institute of Soil Science Chinese Academy of Sciences Department of Agroenvironment and Ecology Agricultural University of Tirana Department of Chemistry Maseno University Center of Life and Food Sciences Technical University Munich

Chlorobenzenes （CBs） are a group of organic pollutants that pose a high environmental risk due to their toxicity, persistence and possible transfer in the food chain. Available data in literature show that CBs axe detected in different environmental compartments such as soil, water, air and sediment. The widespread presence of CBs in the environment is related to their former extensive use in agriculture and industry. Some CBs are ranked in the list of priority pollutants by the Stockholm Convention, and their reduction or elimination from the environment is therefore of high importance. Environmental risk assessment of CBs requires knowledge on the role and importance of the main environmental fate processes, especially in soil. Furthermore, development of remediation strategies for reduction or elimination of CBs from the environment is related to the enhancement of fate processes that increase their dissipation in various environmental compartments. The main objectives of the current review were to present up-to-date data on fate processes of CBs in the soil environment and to explore possible remediation strategies for soils contaminated with CBs. Dechlorination of highly-chlorinated benzenes is the main degradation pathway under anaerobic conditions, leading to the formation of lower-chlorinated benzenes. Biodegradation of lower-chlorinated benzenes is well documented, especially by strains of adapted or specialized microorganisms. Development of techniques that combine dechlorination of highly-chlorinated benzehes with biodegradation or biomineralization of lower-chlorinated benzenes can result in useful tools for remediation of soils contaminated with CBs. In addition, immobilization of CBs in soil by use of different amendments is a useful method for reducing the environmental risk of CBs.

关键词： biodegradation chlorinated benzenes environmental risk immobilization mineralization organic pollutant reductivedechlorination