Thermal stratification effects on MHD radiative flow of nanofluid over nonlinear stretching sheet with variable thickness

Yahaya Shagaiya Daniel,Zainal Abdul Aziz,Zuhaila Ismail,Faisal Salah 한국CDE학회 2018 Journal of computational design and engineering Vol.5 No.2

The combined effects of thermal stratification, applied electric and magnetic fields, thermal radiation, vis-cous dissipation and Joules heating are numerically studied on a boundary layer flow of electrical con-ducting nanofluid over a nonlinearly stretching sheet with variable thickness. The governing equations which are partial differential equations are converted to a couple of ordinary differential equations with suitable similarity transformation techniques and are solved using implicit finite difference scheme. The electrical conducting nanofluid particle fraction on the boundary is passively rather than actively con-trolled. The effects of the emerging parameters on the electrical conducting nanofluid velocity, temper-ature, and nanoparticles concentration volume fraction with skin friction, heat transfer characteristics are examined with the aids of graphs and tabular form. It is observed that the variable thickness enhances the fluid velocity, temperature, and nanoparticle concentration volume fraction. The heat and mass transfer rate at the surface increases with thermal stratification resulting to a reduction in the fluid temperature. Electric field enhances the nanofluid velocity which resolved the sticking effects caused by a magnetic field which suppressed the profiles. Radiative heat transfer and viscous dissipation are sensitive to an increase in the fluid temperature and thicker thermal boundary layer thickness. Comparison with pub-lished results is examined and presented.

Optimization of Power Output Forecasting from Solar PV System using Deep Learning Methods

Yahaya Abdullahi,Bowoo Kim,Dongjun Suh 한국통신학회 2023 한국통신학회 학술대회논문집 Vol.2023 No.2

Dynamic Energy Consumption Forecasting: Exploring the Performance of Machine Learning Algorithms in Dynamic Environment

Yahaya Abdullahi,Bowoo Kim(김보우),Dongjun Suh(서동준) 한국통신학회 2024 한국통신학회 학술대회논문집 Vol.2024 No.1

Hydraulically Actuated of Half Car Active Suspension System

Yahaya Md. Sam,Johari Halim Shah Osman 제어로봇시스템학회 2004 제어로봇시스템학회 국제학술대회 논문집 Vol.2004 No.8

The Evaluation of Nutritive Value of Three Tropical Browse Species for Sheep Using in Vitro and in Vivo Digestibility

Yahaya, M.S.,Kibon, A.,Aregheore, E.M.,Abdulrazak, S.A.,Takahashi, J.,Matsuoka, S. Asian Australasian Association of Animal Productio 2001 Animal Bioscience Vol.14 No.4

In vitro and in vivo experiments were carried out to evaluate the nutritive value of three tropical browse species as assessed by DM and CP digestibility, and NDF and ADF degradability with incubation times (T) of 6, 12, 24 and 48h. During the in vivo digestibility experiment three male castrated sheep (age 16 - 25 months) with a mean liveweight of $11.5{\pm}0.9kg$ were placed in individual metabolism stalls and were allocated to one of the three browse species in a $3{\times}3$ Latin square design. The browse species were all leguminous and consisted of: Acacia sieberina (A. sieberina), Ficus polita (F. polita), and Ficus sycomorus (F. sycomorus). The mean DM and CP contents of F. polita were higher than for A. sieberina and F. sycomorus (p<0.05). In contrast the NDF and ADF contents of F. sycomorus were higher compared to the other species examined (p<0.05). The in vitro DM and CP digestibility, and NDF and ADF degradability observed at different stages of incubation were higher in F. polita followed by A. sieberina and F. sycomorus. The DM and CP digestibility at 48 h incubation were 72.92, 74.84 and 53.52% and 77.38, 77.68 and 63.64% for A. seiberina, F. polita and F. sycomorus, respectively. This shows that F. polita contains more soluble materials which ruminant can benefit from and hence has more feeding value. The fermentation of F. sycomorus was slower for all the nutrients evaluated due to the presence of more fibre. Similarly, higher in vivo digestibility coefficient of DM, CP, NDF, ADF and hemicellulose were observed for F. polita reflecting its higher values of CP, ether extract (EE) and hemicellulose associated with lower values of NDF and ADF. Higher DMI and daily gain were recorded in sheep during feeding of F. polita compared to the other species evaluated. The digestibility of all the nutrients examined were higher in the in vivo than in the in vitro trial except for CP and DM. Sheep showed no visual signs of toxicity throughout the study periods. These results showed A. seiberina, F. polita and F. sycomorus can sustain sheep on a maintenance diet and could as well be used as a supplementary feed to low producing animals during the tropical dry season. Further research is needed to ascertain the viability of using these browse species on a long-term basis.

Evaluation of Structural Carbohydrates Losses and Digestibility in Alfalfa and Orchardgrass during Ensiling 1

Yahaya, M.S.,Kimura, A.,Harai, J.,Nguyen, H.V.,Kawai, M.,Takahashi, J.,Matsuoka, S. Asian Australasian Association of Animal Productio 2001 Animal Bioscience Vol.14 No.12

The evaluation of structural carbohydrate losses and its effect on silages digestibility in alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.) was studied during 5, 21 and 56 days ensiling. About 70 and 60 kg fresh matter of the two forages were ensiled in 9 silos of 120 L capacity. The digestion trials were conducted in two phases using the two grasses in two $4{\times}4$ Latin square design according to the four treatments being the grass and the three silages. There were no differences in the DM and CP contents resulting from 5 to 56 days ensiling in both forages. The water-soluble carbohydrates (WSC), hemicelllose, pectin, and energy were slightly reduced and appeared lower in 56 days silage. The ether extract and cellulose contents slightly increased as the ensiling process advanced in the two species. Hemicellulose losses of 29 and 41 g/kg DM were obtained in alfalfa and orchardgrass, respectively, 56 days after ensiling. While the cellulose losses in both species were very little, compared to that for hemicellulose, the pectin losses, 56 days after ensiling were 15 and 12 g/kg DM in alfalfa and orchardgras respectively. The total structural carbohydrates lost (ie., hemicellulose + cellulose + pectin) in g/kg DM of fresh material forage ensiled, is about four fifths the amount lost by WSC, in alfalfa and about two thirds, in orchardgrass, by 21 days ensiling after the activity of microorganism terminated, indicating that appreciable amount was used as substrate for silage fermentation. Ensiling alfalfa and orchardgrass for 0, 5, 21 and 56 days maintained a decreasing trend of 83.8, 82.5, 79.3 and 78.9% digestibility in alfalfa and 80.5, 77.0, 77.1 and 76.4% digestibility in orchardgrass. While the digestibility of cellulose and ether extract increased in silage in both species, the digestible energy values in silage were reduced from 2.6 to 2.3 and 2.9 to 2.7 Mcal/kg DM respectively in alfalfa and orchard during 5-56 days ensiling.

Review on Magnetic Components: Design & Consideration in VHF Circuit Applications

Yahaya, Nor Zaihar,Raethar, Mumtaj Begam Kassim,Awan, Mohammad The Korean Institute of Power Electronics 2009 JOURNAL OF POWER ELECTRONICS Vol.9 No.2

When converters operate in megahertz range, the passive components and magnetic devices generate high losses. However, the eddy current issues and choices of magnetic cores significantly affect on the design stage. Apart from that, the components' reduction, miniaturization technique and frequency scaling are required as well as improvement in thermal capability, integration technique, circuit topologies and PCB layout optimization. In transformer design, the winding and core losses give great attention to the design stage. From simulation work, it is found that E-25066 material manufactured by AVX could be the most suitable core for high frequency transformer design. By employing planar geometry topology, the material can generate significant power loss savings of more than 67% compared to other materials studied in this work. Furthermore, young researchers can use this information to develop new approaches based on concepts, issues and methodology in the design of magnetic components for high frequency applications.

The Effects of Different Moisture Content and Ensiling Time on Silo Degradation of Structural Carbohydrate of Orchardgrass

Yahaya, M.S.,Kawai, M.,Takahashi, J.,Matsuoka, S. Asian Australasian Association of Animal Productio 2002 Animal Bioscience Vol.15 No.2

This study determined the influence of moisture, ensiling time and their interactions on the losses of hemicellulose and cellulose during ensiling of orchardgrass. Orchardgrass containing 80 (HM), 70 (MM) and 55% (LM) moisture was ensiled in 3 laboratory silos of 500 ml capacity for 3, 7, 21 and 91 days. The dry matter (DM), water-soluble carbohydrates (WSC), hemicellulose and cellulose contents of the ensiled orchardgrass was lowered than that of the untreated grass regardless of moisture content. Ensiling orchardgrass for 91 days (d) decreased (p<0.01) hemicellulose contents from 19 to 15%, 20 to 15% and 18 to 12% and cellulose from 31 to 29%, 29 to 26% and 27 to 26% for LM, MM and HM silage, respectively. Results from fermentation of LM and MM silages were within acceptable guidelines except for butyric acid and ammonia after 3 weeks of ensiling of MM which appeared to be lower than ideal. The results of the fermentation of HM silages were poor showing higher concentration of acetic, propionic and butyric acids and traces of isovaleric, valeric and caproic acids with ammonia at all stage of time. While the DM losses from LM and MM silages over the ensiling period were acceptable, that for HM silage increased to 13% after 91 d ensiling, confirming a poor fermentation process occurred. The greatest WSC losses occurred within 7 d of ensiling and the lowest losses occurred after 3 weeks of ensiling. Except in HM silage, the hemicellulose and cellulose losses were highest (p<0.01) in the first 3 weeks of ensiling. Hemicellulose losses were between 19 and 22% and 4.2 and 5.9% up to 3 weeks and after 3 weeks of ensiling LM and MM silages, respectively. Cellulose losses were small. In contrast, hemicellulose losses after 3 weeks of ensiling of HM silage was about 50% higher than over the first 3 weeks possibly due to clostridial type fermentation. The results showed that increasing ensiling time of high moisture orchardgrass would result in the excessive losses of DM, WSC, hemicellulose and cellulose in the silage.

Partially Observable Markov Decision Processes (POMDPs) and Wireless Body Area Networks (WBAN): A Survey

( Yahaya O. Mohammed ),( Uthman A. Baroudi ) 한국인터넷정보학회 2013 KSII Transactions on Internet and Information Syst Vol.7 No.5

Wireless body area network (WBAN) is a promising candidate for future health monitoring system. Nevertheless, the path to mature solutions is still facing a lot of challenges that need to be overcome. Energy efficient scheduling is one of these challenges given the scarcity of available energy of biosensors and the lack of portability. Therefore, researchers from academia, industry and health sectors are working together to realize practical solutions for these challenges. The main difficulty in WBAN is the uncertainty in the state of the monitored system. Intelligent learning approaches such as a Markov Decision Process (MDP) were proposed to tackle this issue. A Markov Decision Process (MDP) is a form of Markov Chain in which the transition matrix depends on the action taken by the decision maker (agent) at each time step. The agent receives a reward, which depends on the action and the state. The goal is to find a function, called a policy, which specifies which action to take in each state, so as to maximize some utility functions (e.g., the mean or expected discounted sum) of the sequence of rewards. A partially Observable Markov Decision Processes (POMDP) is a generalization of Markov decision processes that allows for the incomplete information regarding the state of the system. In this case, the state is not visible to the agent. This has many applications in operations research and artificial intelligence. Due to incomplete knowledge of the system, this uncertainty makes formulating and solving POMDP models mathematically complex and computationally expensive. Limited progress has been made in terms of applying POMPD to real applications. In this paper, we surveyed the existing methods and algorithms for solving POMDP in the general domain and in particular in Wireless body area network (WBAN). In addition, the papers discussed recent real implementation of POMDP on practical problems of WBAN. We believe that this work will provide valuable insights for the newcomers who would like to pursue related research in the domain of WBAN.

Review on Gallium Nitride HEMT Device Technology for High Frequency Converter Applications

Yahaya, Nor Zaihar,Raethar, Mumtaj Begam Kassim,Awan, Mohammad The Korean Institute of Power Electronics 2009 JOURNAL OF POWER ELECTRONICS Vol.9 No.1

This paper presents a review of an improved high power-high frequency III-V wide bandgap (WBG) semiconductor device, Gallium Nitride (GaN). The device offers better efficiency and thermal management with higher switching frequency. By having higher blocking voltage, GaN can be used for high voltage applications. In addition, the weight and size of passive components on the printed circuit board can be reduced substantially when operating at high frequency. With proper management of thermal and gate drive design, the GaN power converter is expected to generate higher power density with lower stress compared to its counterparts, Silicon (Si) devices. The main contribution of this work is to provide additional information to young researchers in exploring new approaches based on the device's capability and characteristics in applications using the GaN power converter design.