Testing Methodologies for Power Electronic Devices With focus on MOSFETs and IGBTs

Metal Oxide Semiconductor Field Effect Transistor (MOSF ET s) and Insu-lated Gate Bipolar Transistor (IGBT s); both are the state-of-the-art semiconductor switching devices.In this study an in-depth study of Metal Oxide Semiconductor (MOS) physics, cell structure and electrical characterization of MOSFETs and IGBTs has been con-ducted. The aim is to achieve a further improvement on the reliability and rugged-ness of these power electronic devices using findings of the research. These power devices have an extensive industrial and domestic applications, they are the building blocks of nearly all types of power electronic circuits, control systems and advanced digital data storages, laptop and phone chargers, motor drives in electric vehicle, PV converters, Wind converters, industrial heaters. Power electronic monitoring systems including DC to DC converters, DC to AC inverters, AC to DC rectifiers and AC to AC converter.Silvaco simulation and MATLAB modeling enabled the research to gain a vivid understanding of device operation MOS physics and all relevant electrical charac-teristics. The practical experiment side of the research includes high power semi-conductor devices characterization; testing of fabricated discrete devices comprising:(200V, 40A Silicon MOSFET; 1.2KV, 19A Silicon Carbide MOSFET; 600V, 20A and 40A Silicon IGBT; 1.2KV, 25A Silicon IGBT). Consequently, the research work gained an insight to the semiconductor switching latest technologies that are useful for the optimization consideration of power electronic devices. Observations from published journals enabled to see the existing relevant research gaps and works car-ried out by other scientists around this field area. Silicon is the working material for this master’s by research thesis. Moreover, this paper also looks into the great benefits of using silicon-carbide as a material for the next generation technological innovations.Therefore, this research contributes towards device optimization in the following way:Firstly, at a single cell design level. Shielded trench gate geometry architecture outperforms planar gate structure. Secondly, fabricating using a Wide-band-gap material (WBG) enhances device performance greatly

Arbuscular mycorrhiza effects on Faidherbia albida (Del.) A. Chev. growth under varying soil water and phosphorus levels in Northern Ethiopia

Tree seedling establishment, survival and growth in dryland areas is greatly impacted by water, land use effects and soil nutrient availability. Arbuscular mycorrhizal fungi (AMF) can have a substantial effect on water and nutrient uptake by seedlings and are affected by nutrient application, water availability and inoculum source. In this study, we examined the effect of AMF inoculation, phosphorus application levels, soil water status, and inoculum source on the growth of Faidherbia albida seedlings. Two greenhouse experiments were conducted on F. albida seedlings: to compare (a) ±AMF inoculation, at three levels of volumetric soil water content (field capacity (FC), 60% of FC and 20% of FC), and three AMF inoculum sources (derived from cultivated land, grazing land and area exclosure); (b) ±AMF inoculation, at four levels of phosphorus application (0, 25, 50 and 100 mg kg−1) and three AMF inoculum sources. Inoculation with AMF, higher soil water and higher P application significantly increased the growth of seedlings (P < 0.05). F. albida seedlings responded positively to increased water levels. The highest growth and AMF colonization of seedlings was recorded under the lowest water stress with AMF inoculum from area exclosure followed by grazing land inoculum source. The lowest growth was recorded under the highest water stress and cultivated land inoculum source. Plant growth and biomass were positively correlated with increased soil P application, however, AMF colonization decreased with increasing P application. Applying P and inoculating F. albida seedlings with indigenous AMF under low water stress enables optimum plant growth improvement in dryland farming systems

Can rangelands gain from bush encroachment? Carbon stocks of communal grazing lands invaded by Prosopis juliflora

This research article published by Elsevier Ltd., 2017Rangeland ecosystems are rapidly declining due to overgrazing and bush encroachment. Little is known about how important bush encroachment is for climate change mitigation. We estimated woody plant biomass at different Prosopis juliflora cover to quantify above- and below-ground carbon (C) stocks in Afar, northern Ethiopia. We developed allometric models to estimate aboveground biomass (agB) through destructive harvesting based on crown diameter (CrD), diameter at stump height (DSH), and tree height (H) for twenty P. juliflora and 18 Acacia senegal trees. DSH showed the best model fit in predicting above ground biomass compared to H, CrD, and the combination of those predictor parameters, respectively. Models were highly significant for all agB components. Total C stocks of the entire woody species community were about 40% higher (86 Mg C ha−1) at high than at low (50 Mg C ha−1) P. juliflora encroachment categories. We conclude that allometric models using simple dendrometric parameters are highly valuable for assessing P. juliflora biomass. While in lightly invaded areas, eradication and prevention of further spread might be possible, we propose that the high C stocks of rangelands densely invaded by P. juliflora, where eradication attempts have failed, should be considered for potential C trade measures

Variations in soil properties and native woody plant species abundance under Prosopis juliflora invasion in Afar grazing lands, Ethiopia

This research article published by Springer Nature, 2020Introduction Pastoralism and agro-pastoralism are the major modes of life in arid and semi-arid rangelands. However, rangeland quality and quantity are rapidly deteriorating due to a number of natural and human-induced factors, one of which is bush encroachment. Little is known on how bush encroachment affects the ecosystem functions and services expressed in terms of the native vegetation composition and structure, status of the soil seed bank, soil chemical and physical properties, and the abundance of mycorrhiza spores. Methods We assessed woody species in 64 plots distributed across four levels of Prosopis juliflora invasion (high, medium, low, and none) at two sites, Amibara and Gewane, in the Afar Region, Ethiopia. We collected composite soil samples to investigate the soil seed bank, mycorrhizal associations, and spore abundance. Results Plant biodiversity was generally low, with eight and four woody species in Gewane and Amibara, respectively. Prosopis juliflora was dominant in highly, moderately, and lowly invaded areas while Acacia senegal dominated the non-invaded areas. The average number of P. juliflora individuals ranged from 3/ha at non-invaded areas in Gewane to 4200/ha at highly invaded areas in Amibara while the total individual number of native woody species ranged from 0 to 88/ha at highly and lowly invaded areas, respectively. The population structure of trees/shrubs in all invasion areas showed an inverted J-shaped distribution, characterized by a high abundance of small individuals. Prosopis juliflora invasion was associated with high soil OC, Na, Ca, P, bulk density, and moisture content. Herbaceous seed numbers and species richness were highest in the moderately and highly invaded areas. All sampled tree species were associated with mycorrhiza but the percentage of root length colonization by different arbuscular mycorrhizal fungus structures varied significantly (p < 0.05) across invasion categories and sites. Conclusions Our results revealed that although P. juliflora invasion negatively impacted the availability of native woody livestock forage species, it had a positive effect on most soil physical and chemical properties. Such variable effects call out for sustainable management practices when invaded areas are restored

Missions come home

Recorded in Wyneken Hall, Wednesday, January 5, 2000. The missionary field is on our back door step as the face of America changes

062. Ephesians 1:3-6

Chapel Sermon by Yohannes Mengsteab from Ephesians 1:3-6 on Tuesday, January 4, 2000

Evaluation of the Regenerative Potential of a Bioengineered Ligament

The goal of this work was to evaluate the regenerative potential of bioengineered ligaments in a rabbit ACL reconstruction model. Bioengineered ligaments, composed of poly (l-lactic) acid (PLLA) microfibers, were fabricated by braiding and the effect of growth factor and bone marrow aspirate concentrate therapy to enhance regeneration on this matrix was assessed. To achieve this goal, three specific aims were undertaken: 1) development of a braiding machine to fabricate scalable bioengineered ligaments, 2) evaluation of the osteointegration of bioengineered ligaments with and without bone morphogenetic protein-2 (BMP-2) supplementation, and 3) evaluation of the effect of materials, bone marrow aspirate concentrate, and growth factors on the regenerative properties of bioengineered ligaments. Herein, we achieved the fabrication of a bioengineered ligament with a peak load up to 2500 N. Secondly, we found that the osteointegration of the bioengineered ligament in the bone tunnel is predominately anchored by Sharpey fibers, but that BMP-2 supplementation through saline injections did not promote greater bone formation in the bone tunnels. Third, the importance of surgical technique in the fixation of a bioengineered ligament in a rabbit ACL model was found with significantly improved results when fixing the graft in flexion. Additionally, the mechanical properties of the bioengineered ligament were the highest reported in a rabbit ACL model at 12 weeks. Furthermore, it was shown that a bioengineered ligament composed of an 83:17 blend of PLLA and polyethylene terephthalate demonstrates significantly higher mineral apposition rates compared to PLLA alone, which is hypothesized to be a consequence of reduced acidic byproducts. Finally, it was found that the regeneration of the bioengineered ligament undergoes a mechanism of endochondral ossification in the bone tunnel and that BMAC therapy promotes the presence of chondrocyte-like cells within the fibers of the ligament. It is theorized that the compressive forces placed on cells during tensile loading coupled with the low oxygen tension environment promoted the endochondral ossification seen. Overall, this work uncovers the mechanism of regeneration for bioengineered ligaments and provides evidence for the potential of complete bone tunnel regeneration