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On the dynamics of the Tent function-Phase diagrams
(Modem Science Publishers, 2016-05) Kwabi P. A.; Obeng Denteh, William; Boadi, Richard Kena; Ayekple, Yao Elikem
This paper focuses on the study of a one dimensional topological dynamical system, the tent function. We give a good background to the theory of dynamical systems while establishing the important asymptotic properties of topological dynamical systems that distinguishes it from other fields by way of an example - the tent function. A precise definition of the tent function is given and iterates are clearly shown using the phase diagrams. By this same method, chaos in the tent map is shown as iterates become higher. We also show that the tent map has infinitely many chaotic orbits and also express some important features of chaos such as topological transitivity, boundedness and sensitivity to change in initial conditions from a topological viewpoint.
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A MATHEMATICAL MODEL OF COVID-19 TRANSMISSION DYNAMICS WITH EFFECTS OF AWARENESS AND VACCINATION PROGRAM
(Journal of Ghana Science Association, 2023-10) Agbata, B.C.; Shior, M.M.; Obeng-Denteh, W.; Omotehinwa, T.O.; Paul, R.V.; Kwabi P. A.; Asante-Mensa, F
This study introduces a deterministic mathematical model for understanding the transmission dynamics of COVID-19, con sidering the influence of vaccination and awareness program, which target susceptible individuals. The model is based on a system of differential equations, resulting in an SVEIR model. Through qualitative analysis, various aspects of the model, such as disease-free equilibrium, endemic equilibrium, basic reproduction number, and local and global stability, were thoroughly explored. The disease-free equilibrium is proven to be both locally and globally stable when R0 < 1, while it ∼becomes unstable when R0 > 1. Simulation results demonstrate that the combination of vaccination and awareness programs emerges as the most effective approach to mitigate the spread of COVID-19 within the population.
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Molecular characterization of interactions between the D614G variant of SARS-CoV-2 S-protein and neutralizing antibodies: A computational approach
(Infection, Genetics and Evolution, 2021) Kwarteng, Alexander; Asiedu, Ebenezer; Sylverken, Augustina Angelina; Larbi, Amma; Sakyi, Samuel Asamoah; Asiedu, Samuel Opoku; 0000-0002-0893-2908; 0000-0003-2867-1984; 0000-0002-7691-914X; 0000-0002-3814-6924; 0000-0001-5168-4762; 0000-0002-0352-3195
The D614G variant of SARS-CoV-2 S-protein emerged in early 2020 and quickly became the dominant circulating strain in Europe and its environs. The variant was characterized by the higher viral load, which is not associated with disease severity, higher incorporation into the virion, and high cell entry via ACE-2 and TMPRSS2. Previous strains of the coronavirus and the current SARS-CoV-2 have demonstrated the selection of mutations as a mechanism of escaping immune responses. In this study, we used molecular dynamics simulation and MM-PBSA binding energy analysis to provide insights into the behaviour of the D614G S-protein at the molecular level and describe the neutralization mechanism of this variant. Our results show that the D614G S-protein adopts distinct conformational dynamics which is skewed towards the open-state conformation more than the closed-state conformation of the wild-type S-protein. Residue-specific variation of amino acid flexibility and domain specific RMSD suggest that the mutation causes an allosteric conformational change in the RBD. Evaluation of the interaction energies between the S-protein and neutralizing antibodies show that the mutation may enhance, reduce or not affect the neutralizing interactions depending on the neutralizing antibody, especially if it targets the RBD. The results of this study have shed insights into the behaviour of the D614G S-protein at the molecular level and provided a glimpse of the neutralization mechanism of this variant.
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Blood collection tubes impact expression of activated CD4+ and CD8+ T cells in human whole blood assay
(Scientific African, 2023) Kwarteng, Alexander; Osei-Poku, Priscilla; Antwi-Berko, Daniel; Sylverken, Augustina Angelina; Larbi, Amma; Nsiah, Kwabena; 0000-0002-0893-2908; 0000-0002-9187-2503; 0000-0001-8994-1349; 0000-0002-7691-914X; 0000-0002-3814-6924; 0000-0001-8500-0963
Background T-lymphocyte subsets CD4 and CD8 play important role in host immune responses. However, little attention has been given to the impact of time lapse and the various anticoagulant blood collection tubes on the expression frequency and activation status of CD4+ and CD8+ T cells. To this end, we explore the impact of time (t<1 h and t=4 h) and collection tubes (EDTA and heparin) on the expression frequency and activation status of CD4+ and CD8+ T cells among healthy Ghanaian individuals. Methods A cohort of healthy individuals (n=9) is recruited, and blood samples obtained in Ghana for the frequency of CD4+and CD8+ T cells at various time points (<1 h and 4 h). The proportions of activation of these immune markers were profiled using immunophenotyping. Results Significant statistical differences in the activation frequency of CD69 expressing CD4+T cells (t < 1 h and t=4 h; p=0.02) and CD69 expressing CD8+ T cells from EDTA tubes at times (t < 1 h and t=4 h; p=0.05) was observed. No significant difference were observed with CD69 expressing cells in Heparin tubes. Notably, CD8+ T cell activation frequency was observed to be consistently higher than that of CD4+ T cell at the various study time points and in the collection tubes used. No marked alterations were observed witth the proportion of CD4+ and CD8+ T cells in the samples collected at the time points; <1 h and at 4 h. Conclusion The study shows that activation of CD4+ and CD8+ T cells in EDTA tubes differed significantly between both time points (t <1 h and t=4 h) but not in the heparin collection tubes. Therefore, it is important to take into account the elapsed time and the type of blood collection tubes when performing phenotypic characterization of activated immune markers.
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Enhancing Biogas Recovery from Anaerobic Co-digestion of Human Excreta and Food Waste using Response Surface Method and Biochar Additives
(KNUST, 2023-09) Peprah, Blissbern Owusu
Ghana shares similar challenges with other developing nations regarding waste management and access to clean energy. Fortunately,these two challenges are connected. A better waste management strategy would involve converting the organic waste fractions into biogas. Nevertheless, a thorough study of the physico-chemical characteristics of the feed stocks used in the anaerobic digestion process is essential to maximize the energy potential. Consequently, the first phase of this study examined the physical chemical properties of some selected feedstocks, namely, human excrement (HE), food leftovers (FLO), kitchen residues (KR), and cowdung (CD) of Ghanaian origin using APHA standards and equipment. Results of volatile-to-total solid ratios (VS/TS), 0.97±0.001, 0.89±0.001, and 0.85±0.001 for HE, FLO,KR and CD, respectively, showed that all feed stocks had high biodegradable content. though thecarbon-to-nitrogen(C/N)ratiosforFLO(22.14±0.26),KR(23.34±0.25) and CD(26.19±0.47)werewithintheoptimalrange,thatofHE(8.29±0.09)was significantly low.Withameanalkalinityof1219.67±1.53,630.00±0.58,590.00± 2.08 and15,730.00±6.00mgCaCO3 eq./L forHE,FLO,KRandCDrespectively, it wasobservedthatonlyCDhastheoptimalalkalinityvalueforanaerobicdiges- tion. Thisbroughtintoperspectivetheneedforco-digestion.Thesecondphaseof the study,therefore,soughttoprovethehypothesisthatanaerobicco-digestionofHE, FLO andKRcouldgeneratemorebiogaswhileremainingstableifpositivesynergis- tic effectsareachieved.Arandomizedternarymixturedesignandaresponsesurface approach wereusedtoascertaintherelationshipbetweensubstratemixture,biogas yield, methaneyield,andsynergy.ThefindingsrevealedthatR9(78.8%HE:11.8% FLO:9.4 %KR)hadthehighestmethaneyieldof764.79mLCH4/gVS andasyner- gistic indexof3.26.Additionally,the3Dresponsesurfaceplotsshowedimportant and sharedinteractionsbetweenHE,FLO,andKRwherebythepredictedresponses increased withincreasingHEandKRfractionsanddecreasedwithincreasingFLO fractions inthesubstratemixtures.Inthethirdphaseofthestudy,theexperimental cumulativemethaneyieldfromtheoptimumanaerobicco-digestionratio,R9,wasfit- ted tofivekineticmodelsandtheconemodelhadthebestfitrecordingan R2 value of 0.9909.Finally,theeffectsofcoconutshell(CCN)andpalmkernelshell(PKN) biochar dosages(3g,6gand10g)ontheanaerobicco-digestionofHE,FLOand KR wereinvestigatedusingbatchmesophilicexperiments.Theresultsshoweddif- ferences inthepeakoccurrencetimesandmethaneyieldswiththebiochar-amended treatments peakingearlierthanthecontroltreatment.Further,methaneyield(456.25 mLCH4/gVS) increasedwhen3gofCCNbiocharwasused,depictinga23.31%in- crease comparedtothecontrol(SM=370.03mLCH4/gVS). However,toohighCCN biochar dosagesof6gand10grestrictedmethaneproductionduetoapotentialstress on theanaerobicdigestionprocessbroughtonbytheaccumulationof H2 competitors of methanogensthatmighthaveclonedontoexcessbiocharandweakeneditsDIET benefit formethanogenesis.Furthermore,themethaneyieldwas368.69mLCH4/gVS, similar tothatofthecontrol(SM)when3gofPKNshellbiocharwasaddedtothe mixture offeedstocks.Nonetheless,methaneyieldincreasedby10.83%whenthe dosage ofPKNshellbiocharusedwasincreasedto6g.Conversely,PKN10gobserved a decreaseincumulativemethaneyield.Theobservedresultsindicatethatmicrobial activityandkineticscouldpossiblyberestrictedbyexcessivedosageofbiochar.This could beattributedtothepossibleadsorptionofvolatilefattyacids(VFAs)sincethe adsorption mechanismofbiocharisnotselective.Hence,higheramountsofadded biochar maynotnecessarilycorrespondtohigherdigestionefficiency.
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Towards Improved Quality and Performance of Cold-Mix Asphalts for Bituminous Pavement Maintenance in Ghana
(KNUST, 2023-02) Boateng, Kwadwo Appiah
Premature failure and poor performance of cold-mix asphalts (CMAs) used in pothole patching and sectional repairs on bituminous roads are very common in Ghana, and yet, for a long time, the problem has remained unaddressed while the material continues to be used. There is, therefore, the need to improve the quality of cold-mix asphalts used in the country in order to achieve a more successful and durable product in road maintenance. To this end, Ghana’s Ministry of Transportation (MOT) Standard Specification for Road and Bridge Works (2007) was reviewed alongside three foreign specifications on CMAs, namely, Asphalt Institute MS 19 (1997), Chevron USA Incorporated Procedure and Nikolaides Specification (1994), to establish possible commonalities and areas of deviations that could impact the field performance of the material. Also, samples from ready-to-use CMA stockpiles at six contractor sites across the country, and failed road patches were investigated. Further, a series of dense-graded cold-mix asphalts, with simplified material proportioning ratios, were proposed and investigated for adoption and use. Lastly, potential improvement in CMA properties, using montmorillonite nanoclay filler, was explored. It was established that Ghana’s MOT Specification lacked specificity and clarity on the subject of CMAs. In the case of the other Specifications, though variations in mixture design and testing protocols existed, there appeared to be a general consensus on the use of different aggregate gradation structures that lead to high field performance. The asphalt contents of the cold-mix asphalt samples taken from the field tended to range between 3% and 6%, with emulsion mixes having the lower values. In addition, the aggregate structures of the mixes were poor, consisted essentially of single-size aggregates with uniformity coefficient values that ranged between 1 and 4. Some specimens compacted in the laboratory disintegrated during conditioning for stability and flow test, suggesting a lack of stickiness and cohesion within the compacted matrix. It, therefore, appears that the early failures characterizing cold-mix asphalts used in maintenance works in the country could be due principally to inadequate aggregate structure and low binder content of the mixes. For improved cold-mix quality, five aggregate gradation blends that meet GHA dense grading requirements, together with the corresponding emulsionto- aggregate ratio, for easy material batching in the field, have been proposed. Montmorillonite nanoclay used as filler increased the optimum bitumen content and improved the stability of the cold-mixes but resulted in significantly high flows. This suggests that their use in cold-mix asphalts has the potential to induce plastic behaviour and render the mixes more rut-susceptible, especially at high temperatures.
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Measurement and Evaluation of Electromagnetic Radiation Exposure from Antennas in Cellular Networks
(KNUST, 2021-07) Akua, Achiaa
Wireless Technology including that of cellular systems uses radio and microwave energy which is nonionizing in nature, generated at base stations for its transmission via cellular antennas and microwave links to accessible areas for subscribers. The nonionizing radiation (NIR) energy is absorbable by living tissues including human skin and thus, becomes harmful when it exceeds certain thresholds. The health risks associated with exposure from base transceiver stations has gained attention as the demand for cellular services increases. This has led to an increase in communication infrastructures (Base Transceiver Stations), ushering some in human inhabitance to improve quality of service, as these services become a vital part of modern lifestyle. An increase in base transceiver stations, leads to increased cellular radiation pollution which is of public concern. It is therefore necessary to investigate the levels of cellular radiation to ensure that it public health safety limits are not violated. In this thesis, NIR level in power density at forty locations involving residential, commercial and University campuses, considering indoor and outdoor scenarios were measured and estimated with a radio frequency (RF) Explorer 6G Combo Spectrum Analyzer. The results were compared with the minimum safety limits of 4.055 W/m^2 for cellular systems in Ghana, formulated by the International Commission and Non-ionizing Radiation Protection (ICNIRP) and enforced by the National Communication Authority of Ghana (NCA). The maximum total level of radiation consisting of a cumulative of all deployed systems was found to be 862.9 (nW/m^2) for residence near base stations during evening hours and 242.6 (nW/m^2) at day time. The maximum and minimum levels recorded for other locations are 3.96 (nw/m^2) and 0.10 (nw/m^2) at residence away from base stations, 118.5 (nW/m^2) and 0.422 (nW/m^2) for commercial areas and 38.92 (nW/m^2) and 4.97 (nW/m^2) at the campuses. A standard deviation of 49.9 at three different sectors of a single base station was achieved. A highest radiation level of 305.6 (nw/m^2) was recorded at 7 pm of the 24-hour indoor measurement, while the cumulative average of 160.5 (nw/m^2) was recorded at the 24th hour. A percentage of the highest 862.9 (nW/m^2) radiation level recorded is less than 1% of 4.055( w/m^2) minimum safety limits recommended by the International Commission on Nonionizing Protection (ICNIRP). Thus, cellular system radiation emissions of the selected locations do not pose any health threat to the general public in their current capacity.