School of Physics and Earth Sciences

Permanent URI for this collectionhttps://koha2.tukenya.ac.ke/handle/123456789/1935

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PESTICIDES: OCCUPATIONAL EXPOSURE AND POTENTIAL IMPACTS ON ECOSYSTEM AND HUMAN HEALTH IN MERU COUNTY, KENYA
(Technical University of Kenya, 2021-03) MARETE, GABRIEL MUTHEE
ABSTRACT This study assessed the usage of pesticides and its impacts on ecosystems and human health through occupational exposure in selected farming communities in Imenti North, Imenti South and Buuri Sub-counties in Meru, Kenya, where horticultural crops including French beans, kales and tomatoes are grown intensively for export and local consumption. The study was done through use of questionnaire distributed to farmers, agricultural extension and health care workers in selected farms in the three Sub-counties. In addition, analysis of pesticide residues by GC-MS in samples of farm soil, French beans, kales and tomatoes, from randomly selected sites in the three Sub-counties was done. The survey established that various pesticides in the classes of organochlorines, organophosphates, carbamates, pyrethroids and fungicides, were used in the three Sub-counties, with the most frequently used ones (>60 respondents out of 173) being parathion, diazinon, permethrin, pirimiphos methyl, carbaryl, deltamethrin, dieldrin, methoxychlor, cypermethrin, propoxur and carbofuran. Some of these including dieldrin, parathion and carbofuran were used illegally because they have been banned. Although most farmers had general information on pesticide usage through various social groups and contact with agricultural extension workers, only 32–43 % of the farmers had received training on pesticide handling and use. Most farmers (65%) had knowledge of safe pesticide handling procedures including reading labels on packages and wearing protective clothing; but many farmers (44% in Buuri, 57% in Imenti South and 60% in Imenti North) did not wear the requisite protective clothing when applying pesticides. Agricultural extension workers (52%) and health care workers (59%) were trained in their work and had at least a certificate level qualification from a tertiary institution. Most agricultural extension workers (95%) and health care workers (71%) had experience of dealing with pesticides and knew how to administer 1st AID against pesticide poisoning, respectively. Farmers (26%) reported experiencing health effects after using pesticides, with most effects being felt after using dimethoate, malathion, carbofuran, carbaryl and heptachlor. There was a statistically significant (p < 0.05) association between various factors (availability of protective clothing, hiring of labourers, farm land size, expenditure on pesticides and expenditure on treatment, respectively) on intoxication from pesticide exposure. Analysis of organochlorine pesticide residues in soil, French beans, Kales and tomatoes sampled randomly from the selected sites found widespread contamination of soils with organochlorine pesticide residues, with total (Σall OCs analysed, in μg/Kg dry weight) ranging from 15.78 – 307.70 in Imenti North, 1.25 – 159.88 μg/Kg in Imenti South, and 14.96 – 106.13 μg/Kg in Buuri. However, organochlorine pesticide residues were not detected in any of the vegetables. Other pesticides, including chlorpyrifos, carbendazine, imidacloprid, acetaprimid, metalaxyl, diazinon, azoxystribin, triadimefon, acephate, thiamethoxim and diuron were found in farm soils, French beans, kales and tomatoes, with concentrations (in μg/Kg dry weight) in soil samples ranging from BDL (metalaxyl and azoxystrobin) – 13,030 (carbendazin). In French beans, kales and tomatoes, the concentrations (in μg/Kg wet weight) ranged from BDL – 290, with the highest being imidacloprid in tomatoes. The pesticide residue levels generally were very low and met the Maximum Residue Limits set by European Union and other countries, and posed no concern to human health. Risk assessment of the residues in terms of estimated daily intakes (mg/Kg BW/day) also confirmed no health risk in the population. However, it is recommended that preharvest intervals for the pesticides should be observed in the three Sub-counties to avoid long term exposure to consumers.
A MULTI-WAVELENGTH STUDY OF MASSIVE STAR FORMING REGION G188.95+0.89 IN PROBING THE DYNAMICS OF MASSIVE STAR FORMATION
(Technical University of Kenya, 2023-11) MARTIN MULE MUTIE, MARTIN MULE
ABSTRACT Massive stars are born in regions that are opaque to optical observations. This is a challenge in understanding the processes that involve their formation. In order to investigate their formations, a multi-wavelength approach in the infrared (IR) to radio wavelengths was employed to probe the environment around the core, where they are formed. To understand the dynamics of massive star formation, we probed the molecular cloud to check the chemical composition, bipolar outflows and detailed measurements of molecular velocity fields. G188.95+089 is the Massive Star Forming Region (MSFR) that was used in our study. The choice of the star-forming region was due to the fact that it is nearby, emits periodic masers and harbours multiple star-forming cores. While there are many tracers that can be utilized to infer the presence of massive star formation, we relied on Class II methanol masers at 6.7 GHz. In executing the multi-wavelength investigation, radio data from the 26 m Hartebeesthoek Radio Astronomy Observatory (HartRAO) dish was used to analyse the observed spectra of 6.7 GHz methanol masers. Interferometric data from the Atacama Large Millimeter/sub-Millimeter Array (ALMA) were used to check molecular line and continuum emissions of the source. Complementary infrared data from WISE, 2MASS, Hi-GAL, GLIMPSE, IRAS and MSX was used to probe the presence of extended sources surrounding the massive star forming region. Results from radio observations showed that the source had five velocity maser features that exhibited average periodicity of 397.6 days and at least two showed evidence of velocity drifts ranging from −2.38 × 10−5kms−1d−1 to +1.88 × 10−5kms−1d−1. One maser feature at 11.45 Km s−1 exhibited a varying spectra with exponential decay as from year 2003 to present. The spectra of the other maser velocity features have varied significantly since detection in 1991. Using ALMA band 6 at ∼ 1.3 mm and band 7 at ∼ 0.93 mm data, we were able to identify eight continuum cores (MM1-MM8) in the source, with masses ranging from 0.40 to 8.20 solar masses. In the ALMA band 7 observations, G188.95+0.89 MM2 was resolved into two continuum cores separated by 0.1 arcsec. The thermal emission of CH3OH (4(2, 2) - 3 (1, 2)) linked with MM2 has a double peak. In MM2, SiO emission has a bow-shock morphology, but high 12CO evidence for an east-west bipolar outflow is provided by emission to the east and west of MM2. SiO emission shows bipolar outflow centered around MM2 core. Using near- and mid-IR color-color diagrams, young sources were detected in this star-forming region. A total of 36 candidate YSOs, were detected within a 60′′ radius of the G188.95+0.89 source. There is an IR cluster made up of nine of these YSOs just outside the UC HII zone. Only the H and Ks bands of the 2MASS data can reveal nine highly red shifted objects. These sources have redder colors than H − K > 2, indicating that the IR cluster is extremely young. It is unlikely that interstellar absorption alone is responsible for the reddening of the vectors; instead, the presence of a circumstellar disc and envelope must account for at least some of the IR excess. Although further investigation is needed, it appears that the velocity drifts were caused by gas falling into the inner radius of the accretion disk surrounding the protostar G188.95+0.89. The variability of 6.7 GHz methanol masers is a confirmation of on going accretion in the source. Although the presence of accretion disks in the source cannot be confirmed with the existing measurements, the identification of outflows is consistent with their existence. The out-flowing material creates shocks when it encounters the quiescent gas of the envelop. The detection of SiO molecular lines is an effective tool for checking for the existence of shocks. The shock waves pushes the gas into ever denser physical states that allow it to cool and fragment more efficiently. We argue that MM2 has a massive multiple (at least binary) of young star objects, but more VLBI observations are needed to confirm that this is indeed the case.
EFFECT OF DEFECTS AND TEMPERATURE ON THE MECHANICAL AND ELECTRONIC PROPERTIES OF NbC AND NbN: A FIRST-PRINCIPLES STUDY
(2023-11-01) MUCHIRI, PERPETUA
Transition metal carbides and nitrides (TMCNs) are materials that have attracted a lot of attention for both theoretical and experimental studies. This is largely attributed to their excellent physical and electronic properties that makes them ideal candidates for technological and industrial applications. This study focuses on the structural, mechanical and electronic properties of Niobium carbide (NbC) and Niobium Nitride (NbN). Also, owing to their fascinating properties, this study investigated the effects of defects and temperature on the mechanical properties of NbC and NbN from first principles. The study also investigated the effects of defects on the properties of the two materials with concentration ranging between (1.56% − 12.5%) and temperature ranging between 300 K – 1500 K. This is crucial since there exist no perfect materials in nature and the materials are used under extreme conditions such as high temperatures and high pressure. The calculations are performed on the rocksalt (RS), zinc blende (ZB) and wurzite (WZ) structures of the two compounds through the density functional theory formalism using generalized gradient functional approximation for the exchange correlation potential. The obtained results show that the pristine NbC and NbN have high values of elastic constants and mechanical properties in the range of 71 GPa – 815 GPa. The values of the mechanical properties among them bulk moduli, shear moduli, Vicker’s hardness as well as Young’s modulus decrease with increasing defect concentration (1.56 % - 12.5 %) and temperature (300 K - 1500 K). The results obtained show that defect concentration of up to 12.5 % does not compromise the structural properties of the materials and hence, they can still be used in various industrial applications. Further, the temperature range of 300 K – 1500 K considered show that the materials are still mechanically stable and can be suitable candidates in harsh environments of high temperature. Consequently, control of defects and temperature especially during synthesis of these materials is important in evaluating their mechanical response that can drive them to be ideal for super-hard and other related applications
EVALUATION OF THE ACCURACY AND REPRODUCIBILITY OF THE PLANNING ISOCENTRE USING AUTOMATIC AND MANUAL COUCH MOVEMENTS
(2023-11-01) MOGIRE, NAOMI
The present study delves into the subject of analyzing the accuracy and reproducibility of the planned isocenter using automatic and manual couch movements, a pivotal issue within the broader context of radiotherapy. This research was driven by the compelling need to ascertain the deviation from the tumor isocenter during the delivery of radiation to cancerous cells and check whether they are within the acceptable clinical tolerance using the AAPM TG-142 protocol. The methodology adopted for this study was hinged on the analysis of the distances between the treatment isocenter from the planned isocenter. The research process involved a detailed collection of shifts using RANDO phantom from three regions of the body (head and neck, thoracic, and pelvic regions) using both automatic and manual couch movements. Sixty shifts; twenty for each region were recorded from where the distances were calculated. The distances offered a more objective evaluation of the accuracy of both couch movements as opposed to the shifts in coordinates. Moreover, the data was analyzed using MS Excel functions that ensured a comprehensive exploration of the topic and an in-depth understanding of the findings. It was found that automatic couch movements were more accurate in reproducing the planned isocenter as compared to manual couch movement techniques. In addition, the present study records a relatively high shift from the planned isocenter for the thoracic region. Only 20% and 17% of the shifts were within the acceptable limits for automatic and manual couch movement respectively compared to the pelvic, head and neck regions whose shifts tolerance was above 70% for both couch movements These results have far-reaching implications for radiation dose delivery as slight deviations from the planned isocenter could potentially lead to an important under dose to the target, which could lead to tumor recurrence and an excessive dosage to healthy tissue, which could have serious repercussions to normal tissues. In conclusion, the findings from this research not only fill a critical gap in the existing literature but also could potentially influence clinical practices and guidelines in the use of couch movements during treatment planning. Future research endeavors could build upon these findings, thereby paving the way for more comprehensive studies in this field.
CHARACTERISATION OF CORNISH-SOUTH ULTRA-COMPACT HII-REGIONS SAMPLE USING THE MeerKAT
(2023-11-01) JUMA, CALVINCE
Ultra-compact HII (UC HII) regions are small and dense ionized regions surrounding massive protostars. They are formed when ultra-violet (UV) radiation from massive protostars ionizes the surrounding neutral hydrogen gas. UC HII regions represent the earliest stages of massive star formation; hence it is important to characterise them for a better understanding of the process of massive star formation. However, the mystery of the birth and early life of massive stars is yet to be solved due to some challenges such as their short lifetimes, rarity, and large distances, in constructing a complete evolutionary sequence. In addition, the massive protostars are born in a dusty environment which results in high extinction caused by dust grains making it challenging to observe the embedded protostars and their immediate environment in optical and infrared wavelengths. This limitation can be partially overcome by using radio observations that is less affected by dust extinction. Thus, the advantage of UC HII regions in studying massive star formation is that they emit strong radio continuum radiation due to the presence of free electrons within the ionized gas, enabling their detection even at large distances by radio telescopes. In this study, the radio data from the MeerKAT (1.3GHz) and CORNISH-South (5.5 GHz) surveys were used to conduct a comprehensive characterization of UC HII regions. The MeerKAT survey provided the opportunity to study these embedded objects at lower frequencies, where dust extinction has a minimal effect. With this data, I was able to estimate the radio spectral indices (𝛼) of 79 samples of ultra-compact HII regions. It was found that 91% of these sources had 𝛼 ranging from −0.1 to 2 between 1.3 GHz and 5.5 GHz thus indicating that they are thermal. The remaining 9% of the UC HII regions had 𝛼 less than −0.1 at radio frequency, which may be interpreted as the presence of non-thermal emission. However, this effect is caused by the fact that the MeerKAT observation is more sensitive to extended emission than the CORNISH-South observation. Further characterisation of these sources involved the determination of brightness temperature at 5.5 GHz (ranges from ~100.5K to ~104K), optical depth (range: 0.0 to 0.1), Lyman continuum fluxes ( peaks between 46.5 < (logNi) < 48.6 photons 𝑠 −1 ), emission measure (range from 106 to 108 pc cm-6 ), electron densities (peaks between 103 and 104 electrons cm−3 ), physical size (ranging from 0.01 pc to 0.05 pc) which were all consistent with UC HII regions. Finally, investigation for the presence of protostars in the UC HII regions sample was investigated by computing their radio luminosities and comparing them with those of protostars. It was found that the UC HII regions sample was not contaminated with any massive protostellar objects (MYSO jets and low-mass stars)
HEAD TO HEAD AND TAIL TO TAIL 180◦ DOMAIN WALLS IN PbTiO3/PbTiO3 FERROELECTRIC THIN FILMS: AN AB INITIO STUDY
(2024-02-23) SIFUNA, JAMES SIMIYU
Charged domain walls (DWs) in ferroelectric materials have gained a lot of interest for a decade now. Large conductivity has been reported at the DWs of insulating ferroelectric materials, and it has lots of applications in actuators, sensors and capacitors. In the prior studies, the origination of this conductivity at DWs and the stabilization procedures of the charged domains remain controversial. Plenty of studies have called for the employment of dopants, oxygen vacancies or other external potentials to screen the polarization discontinuity at the DWs. Unfortunately, these kind of computations in literature cannot be used to answer questions about; the intrinsic critical thickness for stabilizing the two-dimensional conducting layers for the screening of the polarization charges, the spatial extension of the hole and electron gases, or the size of the polarization that would result from the induction of such DWs in an ideal slab. This thesis seeks to elucidate the stabilization of 180◦ head to head (HH) and tail to tail (TT) DWs in an ideal slab. Once this stabilization is achieved, queries on the origin of the conductivity seen in at the DWs and the stabilization of such domains will be a thing of the past. The electronic and structural characteristics of charged domain walls (DWs) in PbTiO3 thin films were determined using first-principles simulations as prescribed by the SIESTA method. At first, it was important to implement a strategy that would take into account the Hubbard (U) and spin-orbit coupling in the SIESTA method. This was important so as to accurately describe the physics of the DWs in this study. To benchmark the strategy implemented herein, calculations were performed on tetragonal IrO2. The lattice constants of IrO2 were found to be in a perfect agreement to experimental results. A difference of the order of 1.5% on the lattice constants was seen in comparison to other well known methodologies like VASP and QUANTUM ESPRESSO. The band structures of IrO2 generated by the implementation in here, VASP and QUANTUM ESPRESSO were identical. This gave the author confidence to use the implementation on the complex HH and TT domains. The polarization ( e PZ j ) in the DWs under this study was computed using the effective Born charges. The polarization was then used to obtain the spatial extension of the hole and electron gases at the DWs. To understand better on how much charge was transferred from the free-surfaces to the DWs in order to screen the depolarizing fields, the author plotted the planar average of the free charge (ρfree(z)). This thesis demonstrates how the formation of two-dimensional electron and hole gases at the free surface and at the DWs may stabilize the highly energetic 180◦ head to head (HH) and tail to tail (TT) DWs in free-standing slabs. The walls’ breadth, ≈ 7 unit cells for TT DW and ≈ 6 for HH DW, was found to be significantly more than what is seen when the domains are configured in their neutral state. With a perfect balance between the bound charges (divergence of polarization) and the screening charges, the distribution of the free charge was electrostatically associated with structural distortions. Examining the DWs in an intrinsic manner, the global charge neutrality expected, was observed. Also to note, was that at the interior of the domains, the polarization profile was astonishingly flat and was found to be 57.26 μC/cm2 for HH and 45.72 μC/cm2 for TT structures respectively. From a practical standpoint, this study provides an alternate explanation for the intriguing discovery of extremely high conductivities at the DWs between two insulating polar materials.

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