A Comparative Study Between Pr1-xSrxMnO3 and Pr1-xCaxMnO3 at 0 ≤ x ≤ 0.30

A. Hassen 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.1

The magnetic, electric, and structural properties of Pr1-x Ax MnO3, where A is Ca and Sr, have been investigated systematically over the range, 0 ≤ x ≥ 0.30, of doping. For x ≤ 0.20, both systems are ferromagnetic insulators (FMI) even at higher applied field (10 T). Within this range of Sr and Ca dopants, the resistivity (ρ) data can be described well by using the polaron hopping model. The Sr-doped compound with x = 0.3 exhibits a metallic behavior at zero applied field and a negative magnetioresistance (MR) at 10 T. On the other hand, the ρ data of the Ca-doped system (x = 0.3) do not show any insulator-to-metal transition at zero field, but undergo insulator-to-metal transition below 125 K at 10 T with large MR. The magnetic ground state of the Sr- and the Ca-doped systems changes from canted antiferromagnetic (CAF) to ferromagnetic (FM) above x = 0.10. A correlation between structural, magnetic and electric properties is suggested. The results are compared to those for similar systems and are summarized in (x-T) phase diagrams. The magnetic, electric, and structural properties of Pr1-x Ax MnO3, where A is Ca and Sr, have been investigated systematically over the range, 0 ≤ x ≥ 0.30, of doping. For x ≤ 0.20, both systems are ferromagnetic insulators (FMI) even at higher applied field (10 T). Within this range of Sr and Ca dopants, the resistivity (ρ) data can be described well by using the polaron hopping model. The Sr-doped compound with x = 0.3 exhibits a metallic behavior at zero applied field and a negative magnetioresistance (MR) at 10 T. On the other hand, the ρ data of the Ca-doped system (x = 0.3) do not show any insulator-to-metal transition at zero field, but undergo insulator-to-metal transition below 125 K at 10 T with large MR. The magnetic ground state of the Sr- and the Ca-doped systems changes from canted antiferromagnetic (CAF) to ferromagnetic (FM) above x = 0.10. A correlation between structural, magnetic and electric properties is suggested. The results are compared to those for similar systems and are summarized in (x-T) phase diagrams.

Magnetic Phase Transition and Variable Range Hopping Conduction of Y1-xSrxCoO3-\delta

A. I. Ali,Bog G. Kim,A. Hassen,김봉주,S. H. Park,Youngsoo Wu 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.5

The structural, magnetic, and electric properties of perovskite Y$_{1-x}$Sr$_{x}$CoO$_{3-\delta}$ have been investigated systematically over the 0.6 $\leq$ $x$ $\leq$ 0.9 range of doping. The refinements of X-ray powder diffraction (XRD) patterns at room temperature indicates that the investigated samples show a unit cell of about 2 $\times$ 2 $\times$ 4 simple perovskite cubes with I4/mmm group symmetry. An antiferromagnetic (AFM) phase is observed for a Sr doping of 0.60 $\leq$ $x$ $<$ 0.775. With a further increase of Sr content, 0.775 $\leq$ $x$ $\leq$ 0.90, a mixture of AFM and ferromagnetic clusters may exist. No metallic behavior is observed for samples investigated in ambient conditions. The resistivity ($\rho$) data can be described using a three-dimensional variable range hopping (VRH) model. The density of states in the vicinity of the Fermi level for all compositions can be roughly estimated by fitting the temperature dependence of the resistivity.

Effect of Tannin and Species Variation on In vitro Digestibility, Gas, and Methane Production of Tropical Browse Plants

Gemeda, Belete Shenkute,Hassen, A. Asian Australasian Association of Animal Productio 2015 Animal Bioscience Vol.28 No.2

Nineteen tanniferous browse plants were collected from South Africa to investigate their digestibility, gas production (GP) characteristics and methane production. Fresh samples were collected, dried in forced oven, and ground and analyzed for nutrient composition. In vitro GP and in vitro organic matter digestibility (IVOMD) were determined using rumen fluid collected, strained and anaerobically prepared. A semi-automated system was used to measure GP by incubating the sample in a shaking incubator at $39^{\circ}C$. There was significant (p<0.05) variation in chemical composition of studied browses. Crude protein (CP) content of the species ranged from 86.9 to 305.0 g/kg dry matter (DM). The neutral detergent fiber (NDF) ranged from 292.8 to 517.5 g/kg DM while acid detergent fiber (ADF) ranged from 273.3 to 495.1 g/kg DM. The ash, ether extract, non-fibrous carbohydrate, neutral detergent insoluble nitrogen, and acid detergent insoluble nitrogen and CP were negatively correlated with methane production. Methane production was positively correlated with NDF, ADF, cellulose and hemi-cellulose. Tannin decreased GP, IVOMD, total volatile fatty acid and methane production. The observed low methanogenic potential and substantial ammonia generation of some of the browses might be potentially useful as rumen manipulating agents. However, a systematic evaluation is needed to determine optimum levels of supplementation in a mixed diet in order to attain a maximal depressing effect on enteric $CH_4$ production with a minimal detrimental effect on rumen fermentation of poor quality roughage based diet.

Effect of Tannin and Species Variation on In vitro Digestibility, Gas, and Methane Production of Tropical Browse Plants

B.S. Gemeda,A. Hassen 아세아·태평양축산학회 2015 Animal Bioscience Vol.28 No.2

Nineteen tanniferous browse plants were collected from South Africa to investigate their digestibility, gas production (GP) characteristics and methane production. Fresh samples were collected, dried in forced oven, and ground and analyzed for nutrient composition. In vitro GP and in vitro organic matter digestibility (IVOMD) were determined using rumen fluid collected, strained and anaerobically prepared. A semi- automated system was used to measure GP by incubating the sample in a shaking incubator at 39°C. There was significant (p<0.05) variation in chemical composition of studied browses. Crude protein (CP) content of the species ranged from 86.9 to 305.0 g/kg dry matter (DM). The neutral detergent fiber (NDF) ranged from 292.8 to 517.5 g/kg DM while acid detergent fiber (ADF) ranged from 273.3 to 495.1 g/kg DM. The ash, ether extract, non-fibrous carbohydrate, neutral detergent insoluble nitrogen, and acid detergent insoluble nitrogen and CP were negatively correlated with methane production. Methane production was positively correlated with NDF, ADF, cellulose and hemi-cellulose. Tannin decreased GP, IVOMD, total volatile fatty acid and methane production. The observed low methanogenic potential and substantial ammonia generation of some of the browses might be potentially useful as rumen manipulating agents. However, a systematic evaluation is needed to determine optimum levels of supplementation in a mixed diet in order to attain a maximal depressing effect on enteric CH4 production with a minimal detrimental effect on rumen fermentation of poor quality roughage based diet.

Characterization of starch and gum arabic-maltodextrin microparticles encapsulating acacia tannin extract and evaluation of their potential use in ruminant nutrition

Festus A. Adejoro,Abubeker Hassen,Mapitsi S. Thantsha 아세아·태평양축산학회 2019 Animal Bioscience Vol.32 No.7

Objective: The use of tannin extract and other phytochemicals as dietary additives in ruminants is becoming more popular due to their wide biological actions such as in methane mitigation, bypass of dietary protein, intestinal nematode control, among other uses. Unfortunately, some have strong astringency, low stability and bioavailability, and negatively affecting dry matter intake and digestibility. To circumvent these drawbacks, an effective delivery system may offer a promising approach to administer these extracts to the site where they are required. The objectives of this study were to encapsulate acacia tannin extract (ATE) with native starch and maltodextrin-gum arabic and to test the effect of encapsulation parameters on encapsulation efficiency, yield and morphology of the microparticles obtained as well as the effect on rumen in vitro gas production. Methods: The ATE was encapsulated with the wall materials, and the morphological features of freeze-dried microparticles were evaluated by scanning electron microscopy. The in vitro release pattern of microparticles in acetate buffer, simulating the rumen, and its effect on in vitro gas production was evaluated. Results: The morphological features revealed that maltodextrin/gum-arabic microparticles were irregular shaped, glossy and smaller, compared with those encapsulated with native starch, which were bigger, and more homogenous. Maltodextrin-gum arabic could be used up to 30% loading concentration compared with starch, which could not hold the core material beyond 15% loading capacity. Encapsulation efficiency ranged from 27.7%±6.4% to 48.8%±5.5% in starch and 56.1%±4.9% to 64.8%±2.8% in maltodextrin-gum arabic microparticles. Only a slight reduction in methane emission was recorded in encapsulated microparticles when compared with the samples containing only wall materials. Conclusion: Both encapsulated products exhibited the burst release pattern under the pH conditions and methane reduction associated with tannin was marginal. This is attributable to small loading percentages and therefore, other wall materials or encapsulation methods should be investigated.

Analytical modelling of congestion for 6LoWPAN networks

Hayder A.A. Al-Kashoash,Fadoua Hassen,Harith Kharrufa,Andrew H. Kemp 한국통신학회 2018 ICT Express Vol.4 No.4

The IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) protocol stack is a key part of the Internet of Things (IoT) where the 6LoWPAN motes will account for the majority of the IoT ‘things’. In 6LoWPAN networks, heavy network traffic causes congestion which significantly affects the overall performance and the quality of service metrics. In this paper, a new analytical model of congestion for 6LoWPAN networks is proposed using Markov chain and queuing theory. The derived model calculates the buffer loss probability and the channel loss probability as well as the number of received packets at the final destination in the presence of congestion. Also, we calculate the actual wireless channel capacity of IEEE 802.15.4 with and without collisions based on Contiki OS implementation. The validation of the proposed model is performed with different scenarios through simulation by using Contiki OS and Cooja simulator. Simulation results show that the analytical modelling of congestion has an accurate agreement with simulation.

An efficient shear deformation theory for wave propagation of functionally graded material plates

Ahmed Boukhari,Hassen Ait Atmane,Abdelouahed Tounsi,E.A. Adda Bedia,S.R. Mahmoud 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.57 No.5

An efficient shear deformation theory is developed for wave propagation analysis of an infinite functionally graded plate in the presence of thermal environments. By dividing the transverse displacement into bending and shear parts, the number of unknowns and governing equations of the present theory is reduced, and hence, makes it simple to use. The thermal effects and temperature-dependent material properties are both taken into account. The temperature field is assumed to be a uniform distribution over the plate surface and varied in the thickness direction only. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The governing equations of the wave propagation in the functionally graded plate are derived by employing the Hamilton’s principle and the physical neutral surface concept. There is no stretching–bending coupling effect in the neutral surface-based formulation, and consequently, the governing equations and boundary conditions of functionally graded plates based on neutral surface have the simple forms as those of isotropic plates. The analytic dispersion relation of the functionally graded plate is obtained by solving an eigenvalue problem. The effects of the volume fraction distributions and temperature on wave propagation of functionally graded plate are discussed in detail. It can be concluded that the present theory is not only accurate but also simple in predicting the wave propagation characteristics in the functionally graded plate. The results carried out can be used in the ultrasonic inspection techniques and structural health monitoring.

Vibration response and wave propagation in FG plates resting on elastic foundations using HSDT

Mokhtar Nebab,Hassen Ait Atmane,Riadh Bennai,Abdelouahed Tounsi,E.A. Adda Bedia 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.5

This paper presents an analytical study of wave propagation in simply supported graduated functional plates resting on a two-parameter elastic foundation (Pasternak model) using a new theory of high order shear strain. Unlike other higher order theories, the number of unknowns and governing equations of the present theory is only four unknown displacement functions, which is even lower than the theory of first order shear deformation (FSDT). Unlike other elements, the present work includes a new field of motion, which introduces indeterminate integral variables. The properties of the materials are assumed to be ordered in the thickness direction according to the two power law distributions in terms of volume fractions of the constituents. The wave propagation equations in FG plates are derived using the principle of virtual displacements. The analytical dispersion relation of the FG plate is obtained by solving an eigenvalue problem. Numerical examples selected from the literature are illustrated. A good agreement is obtained between the numerical results of the current theory and those of reference. A parametric study is presented to examine the effect of material gradation, thickness ratio and elastic foundation on the free vibration and phase velocity of the FG plate.

Nutritive Value of Grasses in Semi-arid Rangelands of Ethiopia: Local Experience Based Herbage Preference Evaluation versus Laboratory Analysis

Keba, Habtamu T.,Madakadze, I.C.,Angassa, A.,Hassen, A. Asian Australasian Association of Animal Productio 2013 Animal Bioscience Vol.26 No.3

We examined the nutritive value of common grass species in the semi-arid rangelands of Borana in southern Ethiopia using local experience based herbage preference (LEBHP) perception and laboratory techniques. Local pastoralists in the study area were asked to identify common grass species and rank them according to the species' preferences and palatability to cattle. The pastoralists listed a total of 15 common grass species which were then sampled during the main rain and cold dry seasons and analyzed for crude protein (CP), Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF) and ash content to verify pastoralists' claim regarding the quality of individual species. The relative feed value (RFV) and dry matter digestibility (DMD) were also calculated using NDF and ADF contents. Spearman's rank correlation was used to examine possible relationships between laboratory results and pastoralists' experience on grass quality. Cenchrus ciliaris, Chrysopogon aucheri, Digitaria milanjiana, Eragrostis papposa and Panicum maximum were the top five species based on LEBHP perception. There were indications of inconsistency in terms of LEBHP perception among the different pastoral communities. The chemical composition of all grass species showed significant (p<0.05) variation between sites, seasons and species. The results showed that the CP values for the Borana rangelands were in the range of 8.7% in the main rain season to 5.1% for the cold dry season. The fiber constituents were relatively low in the main rain season compared to the cold dry season. Overall, Digitaria milanjiana had the highest CP (16.5%) content, while the least was recorded with Heteropogon contortus (10.8) and Aristida adoensis (9.8%) during the main rain season. It seems that the spatial variability of landscapes within the wider geographical regions, soil properties and texture, and land-use patterns probably contributed to site differences in species quality. Generally, the RFV of individual grass species was significantly (p<0.05) varied between and within sites. The ranking of species by pastoralists according to their preferences by cattle was highly correlated with the chemical composition of laboratory results of individual grass species with 'r' values for CP (0.94), ash (0.95), NDF (-0.98), ADF (-0.93) and ADL (-0.93). We suggest the complimentary use of LEBHP and laboratory techniques in evaluating the nutritive quality of rangeland forage species for sustainable animal production.

Actual fatigue reliability of structural material: Vibration efficiency

Hussain, Muzamal,Khadimallah, Mohamed A.,Ayed, Hamdi,Alshoaibi, Adil,Loukil, Hassen,Alsoruji, Ghazi,Tounsi, Abdelouahed Techno-Press 2022 Advances in concrete construction Vol.13 No.4

This paper is concerned with the vibration analysis of middle layer cylindrical shell made of functionally graded material. The outer layers and inner layer are composed of functionally graded and isotropic material respectively. The Rayleigh Ritz method is applied to solve the presented shell dynamics equations. Two configurations are constructed with layers distributions. Fundamental natural frequencies of the three layered cylindrical shell is plotted against the circumferential wave number with different power law exponents. The frequency decreases with the increase of power law exponent. The fundamental natural frequencies first decreases and fall down to its minimum value, after frequencies increases with circumferential wave number. This is due to change in the magnitude of extensional and bending energies of the cylindrical shells. The computer software MATLAB has been employed for the computation of presented frequencies and tested the results obtained in order to assess the accuracy and validity of the cylindrical shell model for predicting the vibration frequencies of cylindrical shell.