School of Pure and Applied Sciences

Permanent URI for this communityhttp://localhost:4000/handle/20.500.12092/1952

Browse

Now showing 1 - 20 of 89

Adsorption evaluation of selected heavy metal ions by aminofunctionalized low-cost adsorbents. A Review
(Global Scientific, 2021-07) T, Nyahanga; N, Ndung’u Samuel; N, Wanjau Ruth; W, Nthiga Esther
Presence of heavy metals in drinking water has significant adverse effects on human wellbeing due to their toxicity nature. Several techniques have been employed to reduce their concentration to permissible levels. In recent years, adsorption has been widely investigated from low-cost adsorbents due to their cost effectiveness and easy in design. The application of amino-functionalized adsorbents for decontamination of wastewater have been reported. Generally, chemical modification of adsorbents has proved to have a higher adsorption capacity. Numerous amino- compounds such as ethylenediamine, 3-aminopropyl triethoxysilane, Triethylenetetramine, Sodium paminobenzoate, Acrylonitrile, Diethylenetriaminepentaacetic dianhydride, Polyaniline, Nitrilotriacetic acid, 3aminopyrazole, N,N - dimethyl benzal aniline, Di (2-picolyl) amine, Ethylenediaminetetraacetic acid etc. grafted on adsorbents in studying equilibrium, kinetic and thermodynamics has been reported. These adsorbents are applied extensively in the removal of heavy metal ions such as Cu2+, Cd2+, Pb2+, Ni2+, Cr3+, Co2+, As5+ among others. The paper reviews the applicability of vast amino-functionalized adsorbents in the study of equilibrium, kinetics and thermodynamic adsorption studies of heavy metal ions from aqueous solutions
Analysis of the Impact of Cross-sectional Data Discrepancies on the Effectiveness of Radiation Shielding Design Using Monte Carlo Codes
(International Journal of Physics, 2019) Kebwaro, Jeremiah Monari
The effect of cross-sectional data discrepancies on the effectiveness of radiation shielding design has been investigated in this paper. The MCNP code with cross-sections from ENDF/B-V and ENDF/B-VII has been used to determine the gamma ray dose equivalent, H*(10), behind a lead glass shield enclosing a slow neutron source. It is observed that the radiative capture gamma ray dose behind the shield is higher when ENDF/B-V cross-sections are used compared to that produced by ENDF/B-VII cross-sections. The discrepancy is due to absence of energetic primary gamma rays when ENDF/B-VII is used. The results show that shielding design using ENDF/B-VII cross-sections could underestimate the shield by a fair margin and compromise safety. It is therefore necessary to consider more than one release of ENDF/B when using lead glass for shielding slow neutron capture gamma rays. The discrepancies need to be addressed in the next releases.
Anti-inflammatory properties of methanolic bark extracts of terminalia Brownii in wistar albino rats
(Innovare academic sciences pvt ltd., 2016-06) Wilton, Mbinda; Wanja, Mbiri J.; Sichangi, Kasili; Kisangau, Patrick; Ngugi, M. Piero
Anti-Pyretic Properties of Methanolic Bark Extracts of Terminalia brownii in Wistar Rats ( Rattus novegicus )
(J Pharmacogn Nat Prod, an open access journal, 2016) Mbinda, Wilton; Kasili, Sichangi; Mbiri, Jane W; Kisangau, Patrick D; Piero, Ngugi M
The conventional drugs used to manage fever are usually not affordable, not easily available and have adverse side effects. Alternative therapeutic agents, like medicinal plant derivatives, should therefore be developed because they have been reported to be more affordable, more readily available and have lesser side effects. Terminalia brownii is traditionally used to manage fever but this ethno-medicinal claim lacks scientific validation. The present study therefore evaluated the anti-pyretic activity of T. brownii in Wistar rats. Fresh bark samples of T. brownii were collected from Kitui County, Kenya. This study used 30 adult male Wister rats that were 2-3 months old and weighing 140-180 g was used for the experiments. Steam-distilled turpentine was the pyrogen used to induce pyrexia and Aspirin was used as the reference drug. The extract reduced the elevated rectal temperatures by between 1.154.38% while aspirin reduced the elevated rectal temperatures by between 0.00-4.85%. The present study showed a significant dose-dependent anti-pyretic activity of methanolic bark extracts of T. brownii hence validating its folklore use as a fever remedy.
Anti-Pyretic Properties of Methanolic Bark Extracts of Terminalia brownii in Wistar Rats (Rattus novegicus)
(Journal of oJ Pharmacognosy & Natural Products, 2016) Mbinda, Wilton; Kasili, Sichangi; Mbiri, Jane W; Kisangau, Patrick D; Piero, Ngugi M
The conventional drugs used to manage fever are usually not affordable, not easily available and have adverse side effects. Alternative therapeutic agents, like medicinal plant derivatives, should therefore be developed because they have been reported to be more affordable, more readily available and have lesser side effects. Terminalia brownii is traditionally used to manage fever but this ethno-medicinal claim lacks scientific validation. The present study therefore evaluated the anti-pyretic activity of T. brownii in Wistar rats. Fresh bark samples of T. brownii were collected from Kitui County, Kenya. This study used 30 adult male Wister rats that were 2-3 months old and weighing 140-180 g was used for the experiments. Steam-distilled turpentine was the pyrogen used to induce pyrexia and Aspirin was used as the reference drug. The extract reduced the elevated rectal temperatures by between 1.15- 4.38% while aspirin reduced the elevated rectal temperatures by between 0.00-4.85%. The present study showed a significant dose-dependent anti-pyretic activity of methanolic bark extracts of T. brownii hence validating its folklore use as a fever remedy.
Antimalarial pyronaridine resistance may be associated with elevated MDR-1 gene expression profiles but not point mutation in Plasmodium berghei ANKA isolates
(African Journal of Biochemistry Research, 2020-08) Kimani, Shadrack Kanyonji; Shume, Jacob Manyiwa
The selection of resistance is inevitable whenever chemotherapy is necessary for pathogen control. Notably, Plasmodium falciparum has developed multifaceted means to overcome the toxicity of nearly all antimalarial medicines. To bypass this challenge, not only should novel drugs be developed, but the resistance mechanisms to new and existing drugs need should be fully explored. Pyronaridine is a companion drug in Pyramax® , a blend of artesunate (ASN)-pyronaridine (PRD) which is the WHO prequalified alternative for malaria treatment in the African setting. However, half-life mismatch predisposes the PRD to swift emergence of resistance especially in high malaria transmission settings. However, there are no well-characterized PRD-resistant parasite lines. Previously, stable PRD- resistant P. berghei ANKA lines were selected by in vivo drug pressure and preliminary results showed crossresistance with quinolines, therefore, hypothetically the activity of PRD and chloroquine or other quinolines may be comparable, hence, the resistance mechanisms may be parallel. Consequently, genetic polymorphisms and expression profiles of PbMDR-1 that could be associated with pyronaridine resistance were examined by PCR amplification, sequencing and transcript quantification by RT-qPCR. The transcripts level increased during resistance selection while translated PbMDR-1 sequence alignment of PRD-sensitive and PRD-resistant was the same, the expression may be linked to PRD resistance but not mutations.
Antimalarialpyronaridine resistance may be associated with elevated MDR-1 gene expression profiles but not point mutation in Plasmodium bergheiANKA isolates
(African Journal of Biochemistry Research, 2020-08) Kimani, Shadrack Kanyonji; Shume, Jacob Manyiwa
Theselectionofresistance is inevitable whenever chemotherapy isnecessaryforpathogencontrol. Notably, Plasmodiumfalciparum has developed multifacetedmeans to overcomethetoxicityof nearly allantimalarial medicines. To bypass this challenge,not only should novel drugs be developed, but the resistance mechanisms tonewandexisting drugs need should be fullyexplored.Pyronaridine is a companion drug inPyramax®, a blend of artesunate (ASN)-pyronaridine (PRD) whichistheWHOprequalifiedalternative for malariatreatment in the Africansetting. However, half-life mismatch predisposes thePRDto swiftemergence of resistanceespeciallyin high malaria transmission settings. However, there are no well-characterized PRD-resistant parasite lines. Previously, stable PRD-resistant P. bergheiANKA lines were selected by in vivo drug pressure and preliminary results showed cross-resistance with quinolines, therefore, hypothetically theactivityof PRDand chloroquine or other quinolinesmay be comparable, hence, the resistance mechanisms may be parallel. Consequently, genetic polymorphisms and expressionprofiles of PbMDR-1 that could be associated with pyronaridine resistance wereexamined by PCR amplification, sequencingand transcript quantification byRT-qPCR.The transcripts level increased during resistanceselectionwhiletranslated PbMDR-1sequence alignment of PRD-sensitive and PRD-resistant was the same, theexpressionmay be linked toPRD resistance but not mutations
Antimicrobial acitivity of extracts from Tephrosiavogelii Hook F.
(Jomo Kenyatta University of Agriculture & Technology (JKUAT), Kenya, 2006) Wanga, B. N.; Akenga, T.; Imbuga, M.; Gitonga, L.; Olubayo, F.; Namungu, P.
The dichloromethane extracts of the root and leaf of Tephrosia vogelii Hook F. (Family: Papilionaceae) grown in Kenya, were subjected to antimicrobial assays against Staphylococcus aureus, Escherichia coli and Fusarium phoseolida. The minimum inhibition concentrations (MIC) ranged between 0.25 to 6.4 μg/ml for all the microorganisms tested. The crude root and leaf extracts were also toxic to the brine shrimps, organisms used as indicators of toxicity (LC50: 0.960; 0.958μg/ml,respectively). Chromatographic separation led to the identification of (6aß, 12aß, 5'ß)-6a, 12a, 4',5'-tetra hydro-2,3-dimethoxy 5'-ß- isopropenyl–furano (3',2': 8,9)-6H-rotoxen-12-one, (rotenone) in 9.75% yield, (roots), and 11.75% (leaves). Characterisation was achieved by use of spectroscopic techniques and comparison with rotenone standard and literature data. Novel HPLC conditions for purification of rotenoids were established. The MIC of rotenone against the tested microbes was found to be 5.2 and 1.0 μg/ml for Staphylococcus aureus and Escherichia coli respectively, while the LC50 against the brine shrimps was found to be 3.20 μg/ml. The findings indicate that the extracts of T. vogelii contain metabolites that have antimicrobial activity comparable to other medicinal plants.
Bayesian Estimation of Parameters of Weibull Distribution Using Linex Error Loss Function
(Canadian Center of Science and Education, 2020-02) Kinyanjui, Josphat Kamau; Kori, Betty Chemutai
This paper develops a Bayesian analysis of the scale parameter in the Weibull distribution with a scale parameter θ and shape parameter β (known). For the prior distribution of the parameter involved, inverted Gamma distribution has been examined. Bayes estimates of the scale parameter, θ , relative to LINEX loss function are obtained. Comparisons in terms of risk functions of those under LINEX loss and squared error loss functions with their respective alternate estimators, viz: Uniformly Minimum Variance Unbiased Estimator (U.M.V.U.E) and Bayes estimators relative to squared error loss function are made. It is found that Bayes estimators relative to squared error loss function dominate the alternative estimators in terms of risk function.
Bioecology of thrips in French bean growing ecosystem in Kenya
(2012-10-31) Gitonga, Linus Muthuri
Studies on the bioecology ofthrips on French beans were carried out at Machakos, Kaguru and JKUAT. The general objectives of this study were twofold, namely to study the biology and population dynamics of thrips on French beans and to identify and evaluate indigenous natural enemies of the thrips. Two thrips species, M sjostedti and F occidentalis were found throughout the year on French bean crops in all localities of the study. Their population peaks occurred at different times in the course of the year. Populations of M sjostedti peaked after the rains while those of F occidentalis occurred during the hot and dry months of the year at all the localities. Studies on the movements of thrips, into and out of the French bean crops showed that colonization by both species begins soon after germination and that both species preferred the flowers to other plant parts. F occidentalis was found to thrive equally well on the leaves, unlike M sjostedti which only inhabited flower buds and flowers. During the pre-flowering phase ofthe crop, M sjostedti were found on the terminal buds from where they moved to the flowers immediately after the onset of flowering. Most first instar larvae emerged from the pods and flowers. Petioles, leaves, flower buds, flowers and pods were used as oviposition substrates by the thrips.to varying extents. Analysis of the spatial distribution showed both species to be significantly aggregated in the respective plant parts. Laboratory studies indicated that developmental period decreased with an increase in temperature for all the stages of M sjostedti and F. occidentalis. Developmental threshold temperatures were calculated as 9.6 and 9.0 for M sjostedti and F. occidentalis respectively. Development from egg to adult required 212.0 and 256.8 Degree Days for M sjostedti and F. occidentalis respectively. However, at 15?C and 300C, mortality rates for all the developmental stages were higher for M sjostedti than F. occidentalis. The highest mortalities were recorded for the first instar larvae for both species, ranging from 15% to 42% and 11 % to 30% for M sjostedti and F. occidentalis respectively. Pre-pupae and pupae had the lowest mortality rates. An indigenous anthocorid bug, Orius albidipennis was found throughout the year in all the three field sites. Studies on the functional responses of 0. albidipennis to M sjostedti showed that more second instar larvae than adult M sjostedti were killed at all the temperature profiles and densities. With increase in temperature, more second instar larvae and adult M sjostedti were killed. High f2 values shows that both Types I and IT functional responses provided good fit for the data at 15?C, 25?C and 28?C. Attack rates also increased with an increase in temperature. Mortality rates of the 0. albidipennis nymphal instars decreased from the first to the 5th instar at all the temperatures. The mortality rates at 25?C were lower than at 20?C and 30?C for all the nymphal instars except the first instar. Temperatures had a significant effect on the pre-oviposition period, which decreased with an increase in temperature. The eggs took long to hatch at 20?C. Developmental periods of each of the nymphal instars decreased with an increase in temperature. An indigenous larval endoparasitoid of thrips, Ceranisus menes, was found throughout the year in the three localities and its population peaks occurred in the late and early months of the year, from October to April. A closer correlation was found between C. menes and F. occidentalis than with M sjostedti. At JKUAT, percentage parasitism, over the entire crop cycle, ranged from 3.5% to 19.5% and peaked in the months of Marchi April. The lowest percentage parasitism coincided with the period of the highest M sjostedti infestation on French beans. Linear regression analysis showed a density dependence relationship between parasitism and larval density. Laboratory experiments showed that C. menes successfully parasitized and completed development in both M sjostedti and F. occidentalis. Developmental times of C. menes in M sjostedti and F. occidentalis were not significantly different.
Biological diversity of the Yala Swamp lakes, with special emphasis on fish species composition, in relation to changes in the Lake Victoria Basin (Kenya): threats and conservation measures
(2003-05) Aloo, P.A.
During the second half of the last century, the Lake Victoria ecosystem has undergone drastic ecological changes. Most notable has been the decline in the populations of many endemic cichlid fishes. The lake has lost nearly 200 haplochromines and one tilapiine, Oreochromis esculentus. The above changes have been attributed to effects of species stocking and, in particular, from predation pressure by the introduced Nile perch, Lates niloticus. Other factors that have led to the decline of the endemic species include intensive non-selective fishing, extreme changes in the drainage basin, increased eutrophication, and the invasion of the lake by the water hyacinth, Eichhornia crassipes. However, the remnants of some species that had disappeared from Lake Victoria occur abundantly in the Yala Swamp lakes (Kanyaboli, Sare and Namboyo). This paper discusses the biodiversity of the swamp and the three lakes and gives suggestions for their conservation
Biological impact of the exotic parasitoid, Diadegma semiclausum (Hellen), of diamondback moth, Plutella xylostella L., in Kenya
(Karatina University, 2006-08) Momanyi, Caleb; Loehr, Bernhard; Gitonga, Linus
Diadegma semiclausum (Hellen) was introduced to Kenya from Taiwan for the control of diamondback moth (DBM), Plutella xylostella L., and released for the first time in July 2002. Seven and twelve months after release, field mortality studies using the cage exclusion method were conducted at two release sites (Werugha/Taita Hills and Tharuni/Central Kenya). Four treatments were applied: fully closed and partially open cages, both with and without glue applied to the base of the plants for the exclusion of crawling predators. During this time interval, parasitism of exposed larvae rose from 15 to 60% at Werugha and from 8 to 18% at Tharuni, with a concomitant decrease of parasitism by indigenous parasitoids. Crawling predators did not seem to have an effect on mortality. Unexplained mortality increased by half between the first and second experiment at both sites, indicating additional mortality due to the parasitoid. A subsequent field simulation with different parasitoid populations showed that in the presence of parasitoids more larvae died because of abandoning the plant than due to parasitism. Dissections of larvae on the ground showed most were parasitized. Thus, it appears that mortality due to D. semiclausum is more than twice the measured rate of parasitism. Additional information on parasitism was collected from concurrently executed DBM yield loss trials. Parasitism by D. semiclausum was in the same range as in the cage exclusion method. Seven months after release, local parasitoids were present at Werugha and dominant at Tharuni, after one year, they were almost completely displaced at both locations.
Catalytic degradation of methylene blue by iron nanoparticles synthesized using Galinsoga parvifora, Conyza bonariensis and Bidens pilosa leaf extracts
(Springer Nature Switzerland, 2019-09) Makhanu, David Sujee; Kareru, Patrick Gachoki; Wanakai, Sammy Indire; Madivoli, Edwin Shigwenya; Maina, Ernest Gachui; Nyabola, Augustine Otieno
Green synthesized metallic nanoparticles are environmentally friendly, bio-compatible, and highly stable. The aim of this study was to synthesize iron nanoparticles (FeNPs) from FeCl3 solution using aqueous leaf extracts of Galinsoga parvifora (Gp), Conyza bonariensis (Cb) and Bidens pilosa (Bp) and use them in degradation of methylene blue dye. The iron nanoparticles were characterized using UV–Vis spectrophotometer, FT-IR spectrophotometer, X-ray Fluorescence (EDXRF), X-ray difractometer (XRD), and scanning electron microscope (SEM). Phytochemical screening for presence of secondary metabolites revealed presence of phenolics, phytosterols and favonoids. The total phenolic and favonoid content in Galinsoga parvifora, Conyza bonariensis and Bidens pilosa leaf extracts were 57.67±1.27, 117.13±0.03, 126.27±0.013 mg Gallic Equivalent/g of Dry Weight (mg GAE/g DW) and 39.00±0.56, 45.50±0.59, 33.13±0.81 mg Rutin Equivalent/g of Dry Weight (mg RE/g DW) respectively. The UV–Vis spectrum of FeCl3 had a shoulder at 320 nm, which disappeared upon addition of G. parvifora, C. bonariensis and B. pilosa extracts confrming formation of iron nanoparticles. Evaluation of iron content of the synthesized nanoparticles revealed that the iron content in G. parvifora, C. bonariensis and B. pilosa extracts was 51, 47 and 44% respectively. XRD data revealed presence of a large amorphous coating that masked iron peaks, though 2 theta values observed have been reported to be of iron oxides. Methylene blue degradation studies revealed that CbNPs, BpNPs and GpNPs synthesized were good biocatalysts as they degraded the dye by 86, 84.3 and 92% respectively. Therefore, green synthesized iron nanoparticles is cost efective and environmentally safe in providing insight in the environmental removal of dyes.
The Challenges of Using Lesson Plan Formats for Effective Teaching of Chemistry in Kisii District, Kenya
(Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS), 2012) Olunga, Maureen Stella
The study sought to review the state of the use of lesson plans by teachers in teaching Chemistry in six secondary school s of Mosocho Division of Kisii District, namely Cardinal Otunga, Mosocho Academy, Raganga, Kioge, Nyatieko and Nyabururu. The research tool used was the questionnaire. The respondents included the headteachers, the heads of the Science departments and Chemistry teachers and, therefore, three types of questionnaires were administered. The Chemistry teachers’ questionnaire sought information regarding the problems that teachers faced in preparing and using the lesson plans. The heads of science department’s questionnaire solicited for information regarding problems they faced in trying to see that teachers prepared and used the lesson plan, if Chemistry teachers in one school used more than one lesson plan format and the format that was found easier to use. The head teachers’ questionnaire was used to collect information on how they carried out their duty of seeing that teachers prepared and used the lesson plan in teaching chemistry. The head teachers also made comments concerning the use of the lesson plan in teaching chemistry. From the findings of the study, it was noted that most teachers used the columnar format and understood the importance of the lesson plan. However, some were completely unable to use the lesson plan. This shows that there is need to employ qualified teachers. The study contributes useful knowledge to scholars and other education stakeholders that may help in improving teachers’ effectiveness in their teaching of Chemistry among other science subjects.
Compatibility of Metarhizium anisopliae isolate ICIPE 69 with agrochemicals used in French bean production
(Journal of Pest Management, 2012-04) Niassy, S.; Maniania, N.K; Subramanian, S.; Gitonga, L.M.; Maranga, R.; Obonyo, A.B.; Ekesi, S.
The compatibility of the Metarhizium anisopliae (Metschnikoff) Sorokin isolate ICIPE 69, which is being developed as a biopesticide for the control of Frankliniella occidentalis Pergande, was assessed under laboratory conditions with 12 agrochemicals including 5 insecticides (thiamethoxam, L-cyhalothrin, imidacloprid, chlorpyrifos, diazinon), 1 botanical insecticide (azadirachtin), 2 acaricides (abamectin, spiromesifen), and 3 fungicides (carbendazim, copper hydroxide, probineb) used in French bean production. The insecticides abamectin and imidacloprid were highly compatible with M. anisopliae; thiamethoxam was compatible, whereas azadirachtin and L-cyahalothrin were toxic to the fungus, adversely affecting vegetative growth and sporulation. The acaricide spiromesifen was moderately toxic, while the fungicides carbendazim, probineb, and copper-hydroxide were very toxic to the fungus. The combination of the M. anisopliae isolate ICIPE 69 with imidacloprid or thiamethoxam did not result in any synergistic or antagonistic effects to larvae of F. occidentalis. However, the combination of lower concentrations of the fungus with thiamethoxam resulted in a shorter lethal time (LT50) compared with individual treatments. Our results suggest that application of the fungus with agrochemicals has to be assessed carefully prior to any field intervention.
Critical temperature and condensate fraction of a bose – einstein condensate trapped in a finite volume
(Centre for Info Bio Technology, 2014) Mukoya, AK; Sakwa, TW; Khanna, KM; Ayodo, YK; Sarai, A; Rapondo, BW; Namwitako, J
Bose - Einstein Condensation, BEC, of an ideal gas is investigated for a finite number of particles trapped in a harmonic potential. The values of the critical temperature for Rb-87, its condensate fraction and the energy per particle are determined. The maxima appear to increase with the number of particles due to the fact that a smaller system has a larger available effective volume which concurs with the behavior of the critical temperatures.
Current Status of Soil-Transmitted Helminths among School Children in Kakamega County, Western Kenya Prevalence and Intensity of Intestinal Parasites in School age Children in Thika District, Kenya
(Hindawi Publishing Corporation, 2016-02-17) Ngonjo, Teresia; Okoyo, Collins; Andove, Julius; Simiyu, Elses; Lelo, Agola Eric; Kabiru, Ephantus; Kihara, Jimmy; Mwandawiro, Charles
Background. School age children are at high risk of soil-transmitted helminth (STH) worldwide. In Kenya, STH infections in children remain high despite the periodic administration of anthelmintic drugs. Our study assessed the prevalence and intensity of STH in primary school-aged children in Kakamega County, western Kenya. Methodology. We carried out a cross-sectional study on a population of 731 children attending 7 primary schools in March 2014. Children aged 4–16 years were examined for STH by the quantitative Kato-Katz technique. Infection intensities were expressed as eggs per gram (epg) of faeces. Findings. Among 731 school children examined for STH, 44.05% were infected. Highest prevalence of STH was in Shitaho primary school where 107 participants were examined and 62.6% were infected with mean intensity of 11667 epg. Iyenga had the least prevalence where 101 participants were examined and 26.7% were infected with mean intensity of 11772 epg. A. lumbricoides was the most prevalent STH species with 43.5% infected, while hookworm infections were low with 1.8% infected. Conclusion. Prevalence of STHs infections in Kakamega County remains high. We recommend guidelines and other control strategies to be scaled up to break transmission cycles.
D-Optimal Designs for Third-Degree Kronecker Model Mixture Experiments with an Application to Artificial Sweetener Experiment
(IOSR Journal of Mathematics, 2014) Kinyanyui, Josphat; Kungu, Peter; Ronoh, Benard; Korir, Betty; rutto, Mike; Koske, Joseph; Kerich, Gregory
This study investigates some optimal designs in the third degree Kronecker model mixture experiments for non-maximal subsystem of parameters, where Kiefer’s functions serve as optimality criteria. Based on the completeness result, the considerations are restricted to weighted centroid designs. First, the coefficient matrix and the associated parameter subsystem of interest using the unit vectors and a characterization of the feasible weighted centroid design for a maximal parameter subsystem is obtained. Once the coefficient matrix is obtained, the information matrices associated with the parameter subsystem of interest are generated for the corresponding factors. We apply the optimality criteria to evaluate the designs.
D-optimal Rotatable Central Composite Designs Constructed through Resolutions
(Mathematical Theory and Modeling, 2016) Kinyua, Margaret; Koskei, Joseph; Kinyanjui, Josphat
Response surface methodology is widely used for developing, improving, and optimizing processes in various fields. A design is of resolution 𝑅 if no 𝑝 factors effect is confounded with any other effect containing less than 𝑅 −𝑝 factors. In this study, a method for constructing second order rotatable designs based on resolution R, in particular resolution III and IV for three and four factors respectively, argumented with star points is presented. Attention is given to the moment matrices and the related information surfaces based on the parameter subsystem of interest on the second-order Kronecker model and their corresponding rotatable Central Composite Designs (CCDs). Weighted Central Composite Designs (WCCDs) are derived by assigning different weights to two portions of the CCD namely the cube and star portion. The derived designs achieve the property of rotatability and high efficiency and are shown to be D-optimal. Experimental runs are reduced hence economical and the resulting designs are improved in terms of optimality and estimation efficiency. The results show that the cube portion is of great importance in D-optimal resolution III design while the two portions are of equall importance in resolution IV design.
Design and optimization of HPLWR high pressure Turbine gamma ray shield
(Nuclear Engineering and Design; Elsevier, 2015-04) Kebwaro, Jeremiah Monari; Zhao, Yaolin; He, Chaohui
This work proposes the optimum gamma ray shield thickness around the HPLWR high pressure turbine for different occupancy periods in the turbine building. Monte Carlo method was employed in the design process and only radioactive nitrogen-16 was considered as the source of radiation. Five grades of concrete (ordinary, magnetite, heavy magnetite, steel magnetite and barite) were used as shielding materials. The isotope source term in the high pressure turbine was estimated by modeling the HPLWR three pass core in MCNP and tracking the inventory using a simple algorithm. The high pressure turbine was thereafter modeled in MCNP with a concrete shield arrayed in layers around it. The surface flux tally and ICRP74 dose conversion coefficients were employed to estimate the dose profile across the shield. For some shielding materials, exponential functions were fitted on the calculated data to extrapolate dose values beyond the model thickness. The optimum shield thickness was determined by comparing the calculated dose profiles with dose limit proposals in the IAEA standard (NS-G-1.13) on radiation protection considerations during nuclear power plant design. It was observed that with a 120 cm thick heavy concrete shield, the turbine building would be safe for most occupancy periods. However for ordinary concrete the shield would require some extension to guarantee safety. For very long occupancy (more than 10 person hours per week), magnetite shield may also require slight extension. It can therefore be concluded that the shield thickness recommended for BWR turbines (which operate on a direct cycle like HPLWR) could be sufficient for HPLWR if high density concretes are used.