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Gebrekidan, S.B.,Kang, To,Kim, Hak-Joon,Song, Sung-Jin Elsevier 2018 Ultrasonics Vol.85 No.-
<P><B>Abstract</B></P> <P>In this paper, a third harmonic was used to investigate microstructural changes in Al6061-T6 due to different fatigue cycles and a relationship between fatigue cycle and third order nonlinearity has been observed. Piezoelectric measurement harmonic generation technique was applied for the specimens with 0%, 55%, 75% and 85% fatigue cycles, respectively. The results shows that the third order harmonics gradually increased up to 55% and rapidly decreased after wards, it was attributed to the behavior of dislocation, dislocation-precipitation interaction and voids with increasing fatigue cycle. Further, it was verified with scanning electron microscope (SEM). We also observed that third order nonlinearity is more sensitive to small change in area of fraction of voids than second order nonlinearity after 55% fatigue life and could be a good candidate to investigate Al6061-T6 specimen with voids.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Third harmonics is used to investigate change in microstructure. </LI> <LI> Third order nonlinearity is more sensitive to small fraction of voids than second order nonlinearity. </LI> <LI> A gradual decrease of nonlinearity is observed after 55% fatigue cycle. </LI> </UL> </P>
Desawi Kiros Gebrekidan,Abate Mekuriaw,John Cameron 연세대학교 빈곤문제국제개발연구원 2020 Asian Development Perspectives (ADP) Vol.11 No.1
This paper investigates household vulnerability to multidimensional poverty in Degu’a Tembien District. Cross-sectional data were collected randomly from 420 households from six rural villages. Vulnerability to multidimensional poverty was estimated using three-step FGLS. Finding shows that, on the one hand, households with greater social capital, financial capital and number of plots tend to be less vulnerable owing to their lower rates of expected multidimensional deprivation. On the other hand, households with better physical capital are found highly vulnerable with lower volatility of expected multidimensional deprivations. The analysis also shows that female-headed households are more vulnerable to future poverty than male-headed households. Household’s who experienced drought, hailed rainfall and pest attack shocks were associated with increased vulnerability. Results also show that households that rely on savings, sale of livestock and formal borrowing of money following a shock were found to be less vulnerable to multidimensional poverty. Overall, 80 percent of households were vulnerable to multidimensional poverty and the probability of experiencing multidimensional poverty in the near future exceeds the current incidence of household multidimensional poverty. This implies the need to focus on reducing household vulnerability through social protection interventions rather than reducing observed multidimensional poverty.
Wang, T. G.,Dong, Y.,Gebrekidan, B. A.,Liu, Y. M.,Fan, Q. X.,Kim, K. H. Springer Science + Business Media 2017 Acta metallurgica sinica Vol.30 No.7
<P>The Cr-Si-N coatings were prepared by combining system of high-power impulse magnetron sputtering and pulsed DC magnetron sputtering. The Si content in the coating was adjusted by changing the sputtering power of the Si target. By virtue of electron-probe microanalysis, X-ray diffraction analysis and scanning electron microscopy, the influence of the Si content on the coating composition, phase constituents, deposition rate, surface morphology and microstructure was investigated systematically. In addition, the change rules of micro-hardness, internal stress, adhesion, friction coefficient and wear rate with increasing Si content were also obtained. In this work, the precipitation of silicon in the coating was found. With increasing Si content, the coating microstructure gradually evolved from continuous columnar to discontinuous columnar and quasi-equiaxed crystals; accordingly, the coating inner stress first declined sharply and then kept almost constant. Both the coating hardness and the friction coefficient have the same change tendency with the increase of the Si content, namely increasing at first and then decreasing. The Cr-Si-N coating presented the highest hardness and average friction coefficient for an Si content of about 9.7 at.%, but the wear resistance decreased slightly due to the high brittleness. The above phenomenon was attributed to a microstructural evolution of the Cr-Si-N coatings induced by the silicon addition.</P>