Department of Physics

The Comparison between Inquiry-Based and Traditional Learning Approaches on the Student Performance in Physics in Kesses Sub- County, Kenya

2026-03-05T12:53:52Z

The Comparison between Inquiry-Based and Traditional Learning Approaches on the Student Performance in Physics in Kesses Sub- County, Kenya Kimiru, Kinyanjui Godfrey; . Samikwo, Dinah C.; Choge, Dismas Physics is one of the science subjects offered in the Kenyan secondary school curriculum. Despite attracting few learners over a long period of time, its performance has been poor as indicated in the Kenya National Examinations Council (KNEC) reports. This study aimed at investigating performance comparison between learners taught using the Inquiry-Based Learning (IBL) approach and those taught using Traditional Learning (TL) approaches in Secondary schools within Kesses Sub- County in Uasin Gishu County. The objective of the study was to compare the performance of students taught Physics using the IBL approach and those taught using TL approaches. The study was based on Experiential Learning theory by Carl Rogers (1969). The IBL approach for this study was an exploratory learning approach, which involves learners performing experiments and sharing results. The target population was 1,009 Form Three Physics students from 47 schools. Stratified random sampling, simple random sampling and purposive sampling were used in this study. Stratified random sampling was used to divide schools into three strata according to their categories. From each stratum, random sampling was used to select schools from the categories; extra county, County and Subcounty schools. The sample size comprised of 282 physics students from sampled schools. A quasi-experimental design was employed where sampled students were divided into control and experimental groups. Pre-tests and post tests were then administered and tests results were analyzed. Collected data was analyzed using softwares which were, SPSS version 25 and the Microsoft Excel 2021 version application programs. The findings showed that performance of learners taught Physics using IBL approach was greater than that of those taught using traditional approaches. The results of the study are expected to be instrumental to curriculum developers at the Kenya Institute of Curriculum Development (KICD) in designing a Physics curriculum that promotes the IBL approach in delivering instructions. The results will also help school administrators and teachers of Physics in coming up with policies that promote use of IBL approach.

Wavelength reuse in passive optical network for polarization based environmental sensing

2025-06-04T07:51:45Z

Wavelength reuse in passive optical network for polarization based environmental sensing Cherutoi, Henry C.; et. al... We propose and experimentally demonstrate a cost-effective technique of optical sensor that utilizes the reused wavelength in the customer’s premises. This has been achieved by utilizing the saturated EDFA to suppress the extinction ratio of the incoming optical signal hence erasing the downstream data allowing for channel reuse. A 1550nm distributed feedback (DFB) laser is directly modulated with a 10 Gbit/s NRZ data signal and used to characterize the erasing functionality of EDFA. The performance evaluation is done for different input power into the EDFA. The EDFA is shown to reduce the extinction ratio of the incoming signal from 6.48 dB to 0.81dB when the input powers of -7.3 dBm and 1.1 dBm were respectively used, therefore facilitating the direct reuse of the downstream carrier. The vibrational sensor was demonstrated at 85 MHz and the signal was fully recovered. These results indicated the ability of the sensor to detect a change in the environment, therefore giving an early warning signal. The optical fiber sensor system proved to be a reliable and cheaper alternative for environmental monitoring utilizing re-used wavelength.

Parameters of Magic-Angle Twisted Bilayer Graphene (MATBG) Superconductors

2025-05-12T08:34:12Z

Parameters of Magic-Angle Twisted Bilayer Graphene (MATBG) Superconductors Kiboi, Dismas Chenge; Kapil, Mohan Khanna In general, a superconducting state is described by three critical parameters, such as, critical transition temperature (Tc), critical magnetic field (Hc), and critical current density (Jc) or density of states at the Fermi surface of the superconductor. In the case of Magic-angle-twisted-bilayer-graphene (MATBG), the angle of twist ( )  kT = Constant between the two layers of graphene is another important parameter since the variation in  changes the value of Tc, and by virtue of the relation between Tc and EF (Fermi energy),  of states ( ) D E F E F the value of F E changes. Change in F E can result in the change in density , and thus it can affect the current density. Hence in MATBG, the magic angle( )  of twist between the graphene layers becomes an essential parameter along with the three parameters ( c T H c , and c J , ) that influence superconductivity in such materials, and the parameters are calculated for MATBG.

ELECTRON-HOLE SUPERCONDUCTIVITY IN BI-LAYER GRAPHENE SUPERCONDUCTORS

2025-05-12T08:28:57Z

ELECTRON-HOLE SUPERCONDUCTIVITY IN BI-LAYER GRAPHENE SUPERCONDUCTORS Chenge, Kiboi D.; et. al... Superconductivity has been discovered in many different types of materials, such as metals, metallic alloys, doped semiconductors, cuprate oxides, heavy fermion superconductors, and so on; and now recently bi-layer and trilayer graphene superconductors. What is common among all these superconductors is that the super-current is due to the frictionless flow of pairs of charge carriers, called Cooper pairs, and the charge carriers can be electrons, holes in pairs, or electron-hole pairs. In this manuscript, the role of electron-hole pairs in determining the superconductivity in bi-layer graphene superconductors is studied theoretically. It is based on the spontaneous inter-layer phase coherence in a bi-layer quantum Hall system studied using graphene layers. The phase coherence state is assumed to be a gas of super-fluid electron-hole pairs whose components (electrons and holes) belong to two different layers which are one above the other and are separated by a dielectric of a very small thickness (d), and the value of d, should be such that the state of phase coherence is not disturbed. For such a superconductor, specific heat (Cv), entropy (S), and transition temperature (Tc) have been calculated and compared with values known so far

ANFIS-Controlled Boost and Bidirectional Buck-Boost DC-DC Converters for Solar PV, Fuel Cell, and BESS-Based Microgrid Application

2025-02-03T07:26:45Z

ANFIS-Controlled Boost and Bidirectional Buck-Boost DC-DC Converters for Solar PV, Fuel Cell, and BESS-Based Microgrid Application Aeggegn, Dessalegn Bitew; et. al... DC-DC converters are essential for integrating distributed energy resources into microgrid (MG) systems. Tese converters are designed to incorporate intermittent renewable energy sources such as solar photovoltaic (PV) panels, fuel cells (FCs), and battery energy storage systems (BESSs) into the grid. However, conventional DC-DC converters have limitations including lower ef- fciency, voltage ripple, insufcient voltage regulation, and compatibility issues. Tis article presents boost and bidirectional buck- boost converters for direct current microgrid (DCMG) applications, employing an adaptive neuro-fuzzy inference system (ANFIS) for control. Tese proposed converter confgurations adeptly manage wide input voltage fuctuations from intermittent sources, consistently supplying power to the DC bus at 500 V and 120 V for boost and buck operations, respectively, with an efciency of 98.8%. Te output voltage result shows that the ANFIS-based boost converter has 10% overshoot as compared to 41% and 50% overshoot in proportional integral (PI) and fuzzy logic controller (FLC), respectively. In both buck and boost modes, the converters’ voltage gain is infuenced by duty ratio adjustments only, not sensitive to dynamic input voltage and fexible manipulation of the output voltage for BESS charging. Moreover, the designed converters accommodate load variations within the MG. To assess the converters’ ability to regulate output voltage efectively, PI, FLC, and ANFIS controllers are implemented and compared. And the ANFIS controller demonstrates superior performance, ofering faster response times and enhanced stability. Evaluations are conducted through simulations in the MATLAB/Simulink environment.

Coherent High-Speed Signal Transmission in Passive Optical Networks

2024-02-09T09:46:38Z

Coherent High-Speed Signal Transmission in Passive Optical Networks Cherutoi, Henry; Waswa, David; Choge, Dismas A comparative study of digital M-ary Quadrature Amplitude Modulation (16-QAM) and QPSK modulationformats for high-speed transmission is presented. Based on VPI optical simulation software. This paper builds a high-bit rate dual polarization (DP) QPSK and16-QAM modulation formats coherent optical transmission system for Passive Optical Networks (PON). Higher-order modulation formats could be used to provide huge data capacity, extended coverage, and long-reach connections. Channel impairments are mitigated by using digital signal processing (DSP) for dispersion compensation, carrier frequency recovery, and carrier phase estimation. The performance of our system is analysed on Bit Error Rate (BER=1e-9), the threshold for a communication system. For a 32-Splitter PON configuration operating with 16-QAM modulation format, a data rate of 80 Gb/s per ONU is achieved after 24km using standard single mode fibre (SSMF). The results indicate that the proposed schemes are a promising solution for coherent high-speed transmission in PONs.

Mechanical and Elastic Properties of Selected 211 MAX Phases: A Density Functional Theory Study

2024-02-08T07:07:46Z

Mechanical and Elastic Properties of Selected 211 MAX Phases: A Density Functional Theory Study ARUSEI, Geoffrey; et al. MAX Phases are a class of ternary materials that have continued to play a greater role in the field of materials science due to their unique properties that bridge the gap between metals and ceramics which have uses in a wide range of applications. However, in spite of these progress, there are still a lot of open questions and properties that needs to be understood. The Mechanical and elastic properties of (Nine) MAX phase materials, namely, Ti2AlC, Ti2AlN, Ti2GaC, Ti2GaN, Ti2PbC, Ti2CdC, Ti2SiC, Ti2GeC and Ti2SnC have been investigated using the density functional theory within the generalized gradient approximations as expressed in Quantum Espresso and VASP codes. The values of elastic anisotropy, Young’s modulus, Poisson ratio and shear modulus revealed that the compounds were indeed stable and ductile. Out of all the nine MAX Phase materials, Ti2PbC and Ti2CdC are more stable than the other considered compounds. The findings of this study suggest that the nine MAX phases are potential candidates in various industrial applications requiring hard materials.

IN SITU TECHNO-ENVIROECONOMIC ANALYSIS OF A ROOFTOP PHOTOVOLTAIC (PV) BACKUP SYSTEM IN THE TROPICAL CLIMATE

2023-02-15T09:33:12Z

IN SITU TECHNO-ENVIROECONOMIC ANALYSIS OF A ROOFTOP PHOTOVOLTAIC (PV) BACKUP SYSTEM IN THE TROPICAL CLIMATE CHERUIYOT, WILKINS KOSGEI Solar PV generators are increasingly being deployed in the built environment as stand-alone or backup power systems to supply electricity either solely or during power outages respectively. Diesel generators (DGs) are applied routinely as standby power systems by many enterprises and institutions, especially in developing countries where power outages are real and frequent due to unstable national grids. The current pursuit of low-carbon and sustainable source of energy places photovoltaic (PV) power system in advantageous position as a substitute for a DG backup system. An existing off-grid 780 Wp PV system installed as a backup power supply in a learning institution in western part of Kenya was studied both experimentally and theoretically. Technical, economic and environmental analyses were carried out to determine its performance under the local outdoor conditions at the site for a period of one year in 2020. Irradiance estimation models were also validated by experimental data to determine appropriate model(s) for the site. Plane-of-array (POA) solar radiation was measured with solar cell sensor installed at the surface of PV modules and a charge controller/inverter unit with the capability to measure and log real time output current (I) and voltage (V) was used to generate I-V characteristic data. PVsyst software was used to simulate the PV system and generate optimized theoretical results for the site which were compared with experimental results. Available energy was determined as 3202.80 kWh/year, average array efficiency of 11.71%, FF of 0.66, array yield of 4.89 kWh/kW, reference yield of 5.51 kWh/kW, capacity factor as 19.8%, annual average performance ratio (PR) as 76.0%, and average array losses as 0.54 kWh/kW. Economic results for the PV system show that the payback time (PBT) is∼ 6.38 years, LCC of $3057.93, levelized cost of energy (LCOE) of0.045 $/kWh and operation and maintenance (O&M) is17.32 $/year. For the diesel generator (DG),PBT was 4.25 years and O&M was 262.80 $/year for a lifespan of 5 years and assuming that it operates 2 hours per day of blackouts, LCC of $7792.75 and LCOE of 0.324 $/kWh. Environmental results show that the total annual amount of CO2 emissions avoided when PV is used instead of DG power backup system was 5.84 tCO2/year giving an average cost parameter (penalty for CO2 generation) of $9.62. Simulation results gave the available energy as 3746.40 kWh/year, reference yield of 5.55 kWh/kW, array yield of 4.18 kWh/kW, array losses of 0.61 kWh/kW, capacity factor as 21.23%, FF as 0.68, PR as 73.6% and PV array efficiency of 13.19%. The average amount of CO2 emission avoided was 7.95 tCO2/year with annual environmental cost of $116.18. Angstrom-Prescott and Iqbal models were found to be the most accurate for the site having the lowest values of mean absolute percentage error (MAPE) of 8.5% and 8.9% and root mean square error (RMSE) of 0.252 and 0.302 respectively. In conclusion, technically, the low FF (<<1) indicate that the system is not operating at its optimum, which can be attributed to how the PV system was installed. The LCOE results show that PV power is cheaper by a factor of seven than that of the diesel generator, and the amount of CO2 avoided is at least 0.44 tCO2/month. The PV power presents net benefits over diesel power in all performance indices evaluated, and hence can be used as a reliable and affordable replacement for DG backup systems in tandem to the global quest to transition to clean and sustainable energy sources and attainment of the SDGs 7 and 13.

Ab initio insights into Graphene-Zirconium disulfide/diselenide heterostructure as electrode material for alkali-ion batteries

2022-03-28T07:26:20Z

Ab initio insights into Graphene-Zirconium disulfide/diselenide heterostructure as electrode material for alkali-ion batteries King’ori, Gladys W.; et. al... In the search for an energy storage medium with higher electronic conductivity, rate performance and moderate volume expansion, van der Waals heterostructures are a promising alternative. Herein, the potential of graphene (Gr) and Zirconium dichalcogenide (ZrX2, X = S, Se) van der Waals heterostructures for applications as battery electrodes is explored using density functional theory (DFT) calculations. Through intercalating alkali ions (Li and K) between the Gr and ZrX2, we obtain low energy activation barriers, indicating that Gr-ZrX2 van der Waals heterostructures can be candidates for high rate performance electrode application. DFT calculations also indicate that the Gr-ZrX2 heterostructure formation is energetically favoured with better volume expansion as compared to bilayer Gr and ZrX2. The calculated open circuit voltage (OCV) for K intercalation was 0.66 V (Gr-ZrSe2) and 0.77 V (Gr-ZrS2), hence suitable for anodic application in Potassium-ion batteries (KIB). The calculated OCV for Li interaction was 2.83 V (Gr-ZrSe2) and 2.95 V (Gr-ZrS2) hence suitable for cathodic applications

INTEGRATION OF VCSEL WITH MODULATED RAMAN PUMP FOR DATA AND CLOCK TRANSMISSION IN OPTICAL COMMUNICATION

2022-03-01T09:30:14Z

INTEGRATION OF VCSEL WITH MODULATED RAMAN PUMP FOR DATA AND CLOCK TRANSMISSION IN OPTICAL COMMUNICATION OSIEMO, DOUGLAS MOMANYI The evolution of ultrafast optical technologies has led to the realization of low cost, low latency and high speed optical networks. Existing telecommunication infrastructure does not provide sufficient capacity to satisfy future demands in terms of extend of coverage, bandwidth and number of served customers. Fibre-optic technology for data transmission is subject to dynamic development fueled by the increasing demand for large bandwidth and reach extension. High capacity VCSELs are the most desired transmitters for data transmission but, they are limited to short distances. Since high powered Raman lasers are compatible with VCSELs, integration of the two unlocks the puzzle of enhanced data and RF clock signal distribution system. First, a 1550 nm VCSEL was directly modulated with 8.5 Gbps data to counter-propagate with modulated backward Raman pump carrying 8.5 Gbps data over a 50.7 km True Wave Reach fibre to realize enhanced full-duplex bidirectional data transmission system. We report error free data transmission with receiver sensitivity of -14.42 dBm, -14.38 dBm and -13.00 dBm for signal analysis with unmodulated backward Raman, modulated backward Raman pump analysis and signal analysis with modulated backward Raman respectively at BER threshold of 10-9. Secondly, unidirectional data transmission system was realized by employing modulated forward Raman pump instead of modulated backward Raman. Modulated Raman pump simultaneously amplifies the VCSEL channel and transmits data over the transmission link, therefore maximizing the network efficiency. Minimum receiver sensitivity of −14.38 dBm was attained for a transmission configuration with un-modulated forward Raman pump. Thirdly, performance of DFB laser on 2 GHz, 4 GHz and 6 GHz RF clock signal distribution was investigated. At 10 kHz offset frequency lowest phase noise of -119.93 dBc/Hz was recorded for 2 GHz signal. Fourthly, we realized a technique of exploiting forward and backward Raman pumping to both disseminate clock tones and amplify data signal simultaneously. 10 Gbps data from directly modulated VCSEL was coupled into a 50.7 km fibre to counter propagate with 4 GHz modulated Raman pump and repeated the same for forward pumping where the data co-propagated with 4 GHz clock. Amplified errorfree data transmission with minimum receiver sensitivity of -14.8 dBm for modulated forward Raman and distributed stable clock signal over 50.7 km True Wave Reach fibre was achieved. A maximum phase noise of -100.6 dBc/Hz at 10 kHz offset frequency was experimentally measured for 50.7 km fibre transmission with backward Raman pumping. Finally, long term stability measurement on RF clock signal was analyzed using Allan deviation for DFB laser. Allan deviation of 1.49e-12 /s and 1.63 e-12 /s was obtained for B2B and 24.69 km fibre respectively at 100 s averaging time for 2 GHz clock signal. The results show the suitability of VCSEL light source and Raman amplification for application in integrated optical transmission links. This work offers an integrated VCSEL-based transmission system which satisfy the requirements for the next generation optical fibre networks regarding long reach, enhancement, duplex data/clock dissemination with a single fibre upstream and downstream transmissions.