KNUSTSpace

Institutional Repository of the Kwame Nkrumah University of Science and Technology

On this portal we showcase the intellectual output of the university..

 

Communities in DSpace

Select a community to browse its collections.

Now showing 1 - 5 of 6

Recent Submissions

No Thumbnail Available
Item
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.
No Thumbnail Available
Item
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.
No Thumbnail Available
Item
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.
No Thumbnail Available
Item
Flexible and Wearable Pattern-Reconfigurable Printed Monopole Antenna for On-Body Communication
(KNUST, 2021-07) Philip, Arthur
The fundamental feature of reconfigurable antenna (RA) systems is the ability to modify its functional operating characteristics compared to conventional antenna systems. As the size of electronic devices continues to shrink with stringent space constraints, reconfigurable antennas provide a low-cost approach for introducing adjustable properties on a single antenna element. This is to eliminate the need for multiple single-purpose antennas in diversity applications. Recently, reconfigurable antennas have gained popularity in wearable devices and finding applications in health care for the diagnosis and treatment of diseases such as stroke and cancer in tissues. Many applications of wearable antennas in personal communication devices, military gadgets and emergency apparatus are continuously growing. It is required that on-body antennas are unobtrusive and highly efficient with conformable features that can be easily suited to the configuration of the human body. However, due to the conductive nature of the human body, up to about 50% of the radiated energy from conventional printed monopole antennas can be absorbed. This effectively renders the omnidirectional antenna unidirectional when mounted on or close to the human body. To this end, this current work proposes a simple technique to convert the conventional monopolar radiation pattern of a printed monopole antenna into a unidirectional radiation. This is shown among other advantages to significantly reduce specific absorption rate (SAR) and achieve circular polarization. The initial process begins with the design of a compact, low-profile, slotted-stepped planar monopole antenna (PMA) at the 2.45 GHz Industrial, Scientific and Medical (ISM) band. Further analysis presents an optimized reconfigurable extension of the antenna based on two switchable RF PIN diodes. This is incorporated in the antenna to asymmetrically steer the radiation pattern at different directions in specific operating modes. It is also shown that the frequency-radiation characteristics linkage that leads to shifts in the frequency while the radiation pattern is adjusted is fully decoupled in this design. Here, the switching effect of the radiation pattern does not cause any significant detuning in the operating frequency. This is further validated at varying antenna positions and excitation levels. To present a conformable form of the reconfigurable antenna, a flexible substrate material is chosen for the design. Flexibility and wearability tests of the antenna are performed at various degrees of bending and subsequent placement on a human phantom model. The on-body effects on the antenna are characterized in simulation and measured on real human body. Simulated results show stable radiation patterns, reflection coefficient (𝑆11<−20 𝑑𝐵) and a circular polarization at 2.45 GHz. Meanwhile, low simulated peak SAR of 0.46 𝑊/𝑘𝑔 and 0.39 𝑊/𝑘𝑔 averaged over 1𝑔 and 10𝑔 of tissue respectively are recorded when the antenna is mounted directly on the human body. This is achieved without the use of conventional large and bulky cavity-backed structures. Hence, the overall size of the antenna measures only a compact square size of 0.235𝜆, making it a very suitable candidate for on-body applications.
No Thumbnail Available
Item
Improving Cell Edge Performance for LTE Network Using 0.8 Ghz and 2.6 Ghz Frequency Bands
(KNUST, 2021-03) Abrokwa, Kofi Kwarteng
To provide maximum Physical Downlink Shared Channel (PDSCH) capacity for cell-edge Long Term Evolution (LTE) customers, the received signal strength from the Base Station (BS) to the User Equipment (UE) should be high. However, increasing power levels at the BS to ensure signal availability for users at the cell edge presents Inter-Cell Interference (ICI) in the LTE network, which drastically impacts the Quality of Service (QoS) negatively. As a solution to curb this problem, researchers have adopted several techniques such as Geometric Factor Model (GFM), Heterogeneous Network (HN), and Power Variation System (PVS) to assign a carrier frequency to users based on their respective distance from the base station to boost the signal at the cell edge. However, these methods do not include the current channel conditions present in a multipath fading environment which are the main concern that needs to be taken into consideration. It is therefore imperative to investigate the performance of the LTE network by considering the impairment in the wireless channel to see its corresponding effect on the user performance. The inclusion of these challenges in the wireless channel will give an idea of the performance of the LTE network and the means to improve it for the optimum benefit for the users. This work presents the performance of cell-edge users in the LTE network on 0.8 GHz low band and 2.6 GHz high band, signal propagation experiment in MATLAB\Simulink environment based on Markov model. Carrier aggregation provides a technique for LTE users to access the network using multiple frequency bands, which have varying penetration losses and enlarged bandwidth for the user. The low and high band frequencies used in this work help the user at the cell edge to achieve coverage and throughput at the same time in the LTE network. The simulated signal-to-noise ratio of the two frequencies achieves a better performance metric for customers to experience a good internet service. The average bit error rate (BER) for users using 0.8 GHz was 5.50e-5 while the average bit error rate for users using 2.6 GHz was 1.98e-4. Cell edge users using 0.8 GHz frequency carrier experienced an average of 92% throughput while those on 2.6 GHz experienced an average of 70% throughput. These results provide a realistic and reliable approach to mitigate cell edge challenges for LTE users than those achieved by other methods such as GFM, HN, and PVS used by earlier researchers.
No Thumbnail Available
Item
Asante Folklore and Kumasi Kiosk Architecture:a Visual Exploration of Hybridity and Mythography
(KNUST, 2009-02) OPPONG, E. T.
This studio-based research improvises on the architectonics of Kumasi kiosks. I present the ensuing body of artefacts as a working prototype which joins on-going cultural conversations on hybridity in contemporary art. The typical Kumasi kiosk is referenced as a site for negotiation of boundaries in its design, setting and function, but I have also made allusions to suggestions of hybridity and boundary negotiation in the polyvalent structure of Asante myth and folklore. I made a close study of three hundred kiosks located in the urban quarters of Kumasi. I also engaged such thinkers on hybrid spaces as Homi Bhabha , Jacques Derrida, Michael Foucault, Stuart Hall, Paul Gilroy, etc, to discourse on Asante mythology. I laid emphasis on the myth of ɔhyeεni (ɔhene-king), a patriarchal figure who negotiates boundaries, Asante and Akan filial kinship narrative from Asante history. I employed a personal technique of painting, -Aberphoh, which is a reconfiguration of abstract expressionist and surrealist genres. Asante art forms laden with their myths, some of which visually portrayed mythology, especially the totems, were also studied as the basis upon which art works were recreated in the form of paintings on sculptural structures created with plywood. I used the Asante myth of Abubu-mmabaa to explore the structural dialogue of inside and outside in my hybridized artefact. I have also presented an iconographic catalogue of totems and symbols which appear on the inner and outer surfaces of my structures. I present my project as an artefact to be contained in a gallery space as well as a structure or site which contains other artefacts. Like the Kumasi kiosk, these structures are not intended to be permanently site-specific. Each is collapsible and foldable and thus portable to any possible location for re-erection and exhibition. It is a cross genre installation interfacing painting, sculpture, architecture, poetry and performance.
No Thumbnail Available
Item
Scattering of kinks in noncanonical sine-Gor Scattering of kinks in noncanonical sine-Gordon Model don Model
(Turkish Journal of Physics, 2022) Takyi, Ishmael; Barnes, Benedict; Tornyeviadzi, Hoese Michel; Ackora-Prah, Joseph; 0000-0002-1217-0889; 0000-0002-0580-5655; 0000-0001-9488-9610
In this paper, we numerically study the scattering of kinks in the noncanonical sine-Gordon model using Fourier spectral methods. The model depends on two free parameters, which control the localized inner structure in the energy density and the characteristics of the scattering potential. It has been conjectured that the kink solutions in the noncanonical model possess inner structures in their energy density, and the presence of these yields bound states and resonance structures for some relative velocities between the kink and the antikink. In the numerical study, we observed that the classical kink mass decreases monotonically as the free parameters vary, and yields bion-formations and long-lived oscillations in the scattering of the kink-antikink system. :