Effects of Thickness Variation in the Multilayer Thin Film on the Performance of Eta Solar Cell

A highly structured eta solar cell of the type TiO2/In(OH)xSy/Pb(OH)xSy/PEDOT:PSS/Au with different layer thickness has been fabricated using various deposition techniques for each layer in the stack. The solar cell parameters, Uoc, FF and 14η">  have been extracted from current- voltage characteristics measurements. The buffer layer and the hole collector layer have been kept constant while the window and the absorber layer have been varied. The thickness of either of the two layers being varied has been observed to affect the performance of the solar cells. The difference in thickness has been attributed to affect the charge lifetime in the space charge region therefore affecting the performance of the solar cell.Keywords: Thin film; TiO2; eta solar cell; photovoltaic; spray pyrolysis; chemical bat

Effects of Annealing Ambient on the Structural, Optical and Electrical Properties of TiO2:Ge Thin Films

TiO2, a semiconducting material with a wide energy band gap, has been researched intensively due to its interesting properties and many potential applications. The films properties can as well be modified by preparing the films under diverse ambient to suit diverse applications. In this work, the effects of the annealing atmosphere on the structural, optical and electrical properties of pure TiO2 and TiO2:Ge composite thin films deposited by sputtering from commercially available pure TiO2 and TiO2:Ge (85:15) targets respectively were studied. The films were deposited on fluorine doped tin oxide glass substrates by radio frequency magnetron sputtering technique at room temperature 23–25 ℃ and then annealed at 450 ℃ for one hour in three different atmospheres: air, argon and nitrogen. The XRD results revealed that, both pure TiO2 and TiO2:Ge thin films were crystalline and had a mixed phase of anatase and rutile regardless of the annealing ambient. The calculated crystallite sizes ranged between 19–21 nm with the particle sizes for TiO2:Ge films being larger compared to pure TiO2 as calculated from ImageJ software. Electrical measurements showed that the resistivity of as deposited pure TiO2 films (about 13.03 × 10–2 Ω-cm) was greater than the TiO2: Ge composite (5.91 × 10–2 Ω-cm). Furthermore, on annealing, pure TiO2 had a resistivity of 9.47 × 10–2 Ω-cm–10.4 × 10–2 Ω-cm, while the TiO2:Ge composite had a resistivity of 2.24 × 10–2 Ω-cm–3.61 × 10–2 Ω-cm depending on the annealing atmosphere. Variation of annealing atmosphere had minimal influence on the electrical resistivity of the films. The films annealed in nitrogen recorded the least resistivity values averaging about 5.86 × 10–2 Ω-cm, while those annealed in argon and air recorded a resistivity of 6.94 × 10–2 Ω-cm and 6.65 × 10–2 Ω-cm, respectively. The transmittance spectra showed that, all the annealed films were transparent in the visible region (400–700 nm) with a mean bandgap of 3.60 eV for each annealing atmosphere. It is recommended that films annealed in nitrogen atmosphere could be considered for potential applications in photovoltaics. Keywords: Titanium dioxide; Germanium; Ambient; Structural; Optical, Electrica

Hepatitis A Antibody Seroprevalence in a Selected Kenyan Pediatric Population

The incidence of infection by Hepatitis A virus shows regional variation being highest in developing countries. Determination of age specific Hepatitis A virus (HAV) seroprevalence and the associated risk factors would help better plan for national preventive strategies including vaccination. We carried out a cross-sectional study on 300 children from Nairobi city, Kenya during the years 2003-2004. The age range of the children was 2 - 14 years and were from low and high socioeconomic status (SES) families. The indicators of SES included employment status, residence, number of children per patient’s household, parents’ level of education and source of drinking water. SES was encoded and analysed using Statistical Program for Social Sciences (SSPS) version 16.0. Seroprevalence increased significantly with advancing age. Seropositivity of HAV antibodies was significantly higher among children of low SES, 77.6% by the age of 14 years compared to children of high SES, 38.9% by the same age. Crowded household and parental education were significantly associated with high seropositivity and seronegativity respectively. There is significant rate of seronegativity amongst the studied population especially those from richer backgrounds making them more susceptible to severe infection in future with concomitant complications. We propose that revision of national vaccination program should be considered to include Hepatitis A vaccination

The Habitats and Biodiversity of Watamu Marine National Park: Evaluating Our Knowledge of One of East Africa's Oldest Marine Protected Areas

Watamu Marine National Park (WMNP) is one of the oldest no-take Marine Protected Areas (MPAs) in the world. Since its establishment in 1968, it has been the subject of a number of scientific studies as well as suffering from a range of modern threats to coastal marine habitats. The current state and conservation value of WMNP is documented in terms of habitat, biodiversity, and available scientific literature. There were 101 published references relating to WMNP found, which mostly focus on coral reef ecology, with less attention to other topics, such as biodiversity, socio-economics, or the ecology of non-coral reef habitats. The habitat map produced of WMNP is the first to show this level of detail and the only habitat map of a Kenyan MPA. Nine habitat categories were mapped; revealing that the most dominant habitat type is seagrass and the least is coral reef. Species lists were collected for fish, echinoderms, molluscs, crustaceans, corals, and seagrass, and species abundances were used to estimate total species richness, species diversity and sampling completeness. There were 18 species across all groups that fall into a category of conservation concern (other than Least Concern or Not Evaluated) on the IUCN Red List and 8 species found which are currently undescribed. The findings of this paper emphasise the importance of non-coral habitats in the WMNP, such as seagrass beds, and the need for more research into the ecology and conservation importance of these habitats. The information provided in this paper provides a comprehensive overview to any scientist or conservationist wanting to carry out further work in WMNP

Different plant viruses induce changes in feeding behavior of specialist and generalist aphids on common bean that are likely to enhance virus transmission

Bean common mosaic virus (BCMV), bean common mosaic necrosis virus (BCMNV), and cucumber mosaic virus (CMV) cause serious epidemics in common bean (Phaseolus vulgaris), a vital food security crop in many low-to-medium income countries, particularly in Sub-Saharan Africa. Aphids transmit these viruses “non-persistently,” i.e., virions attach loosely to the insects' stylets. Viruses may manipulate aphid-host interactions to enhance transmission. We used direct observation and electrical penetration graph measurements to see if the three viruses induced similar or distinct changes in feeding behaviors of two aphid species, Aphis fabae and Myzus persicae. Both aphids vector BCMV, BCMNV, and CMV but A. fabae is a legume specialist (the dominant species in bean fields) while M. persicae is a generalist that feeds on and transmits viruses to diverse plant hosts. Aphids of both species commenced probing epidermal cells (behavior optimal for virus acquisition and inoculation) sooner on virus-infected plants than on mock-inoculated plants. Infection with CMV was especially disruptive of phloem feeding by the bean specialist aphid A. fabae. A. fabae also experienced mechanical stylet difficulty when feeding on virus-infected plants, and this was also exacerbated for M. persicae. Overall, feeding on virus-infected host plants by specialist and generalist aphids was affected in different ways but all three viruses induced similar effects on each aphid type. Specifically, non-specialist (M. persicae) aphids encountered increased stylet difficulties on plants infected with BCMV, BCMNV, or CMV, whereas specialist aphids (A. fabae) showed decreased phloem ingestion on infected plants. Probing and stylet pathway activity (which facilitate virus transmission) were not decreased by any of the viruses for either of the aphid species, except in the case of A. fabae on CMV-infected bean, where these activities were increased. Overall, these virus-induced changes in host-aphid interactions are likely to enhance non-persistent virus transmission, and data from this work will be useful in epidemiological modeling of non-persistent vectoring of viruses by aphids

Comparison of the accuracy of digital models obtained from scans of impressions versus direct intra-oral scans

Magister Chirurgiae Dentium - MChDMeasurements and a variety of analyses of dental casts are essential for precise diagnosis of an orthodontic case. Study models have long been an essential part of orthodontic diagnosis and treatment planning. Currently virtual computerized models are available to clinicians, supplemented by dedicated software for performing needed measurements (Zilberman et al, 2003). Digital impression methods are now available and intraoral digital scanning techniques make it possible to generate study models directly from the scanning of the dentition. The aim of this study was to compare measurements taken after scanning the dental impressions to the measurements obtained from using direct intraoral scanning of the dentition. Alginate impressions of the maxillary and mandibular dentitions were taken on 20 patients and these impressions were scanned using a 3 Shape R 700 TM scanner. Direct intraoral scans of both dentitions were then performed for the same patient. Ortho analyzer TM software was used to measure the mesiodistal widths of individual teeth, and the intercanine and intermolar on digital models of the scanned impressions and digital models obtained from direct intraoral scans of the maxillary and the mandibular dentitions. The results indicated that there were no statistically significant differences between mesiodistal widths, and intercanine and intermolar distances between the two techniques (p > 0.05). Because of the high level of accuracy of the virtual measurements compared to those of the scanned impressions, it can be concluded that direct intraoral scanning of the dentition can be used with confidence in the clinical situation to measure tooth sizes and inter-arch distances for orthodontic purposes. Orthodontists commonly use models for various areas in the practice, clinical research and medico-legal documentation (Marcel, 2001

Three Aphid-Transmitted Viruses Encourage Vector Migration From Infected Common Bean ( Phaseolus vulgaris ) Plants Through a Combination of Volatile and Surface Cues

Bean common mosaic virus (BCMV), bean common mosaic necrosis virus (BCMNV), and cucumber mosaic virus (CMV) are important pathogens of common bean (Phaseolus vulgaris), a crop vital for food security in sub-Saharan Africa. These viruses are vectored by aphids non-persistently, with virions bound loosely to stylet receptors. These viruses also manipulate aphid-mediated transmission by altering host properties. Virus-induced effects on host-aphid interactions were investigated using choice test (migration) assays, olfactometry, and analysis of insect-perceivable volatile organic compounds (VOCs) using gas chromatography (GC)-coupled mass spectrometry, and GC-coupled electroantennography. When allowed to choose freely between infected and uninfected plants, aphids of the legume specialist species Aphis fabae, and of the generalist species Myzus persicae, were repelled by plants infected with BCMV, BCMNV, or CMV. However, in olfactometer experiments with A. fabae, only the VOCs emitted by BCMNV-infected plants repelled aphids. Although BCMV, BCMNV, and CMV each induced distinctive changes in emission of aphid-perceivable volatiles, all three suppressed emission of an attractant sesquiterpene, α-copaene, suggesting these three different viruses promote migration of virus-bearing aphids in a similar fashion