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BEST RANDOM PROXIMITY PAIR THEOREMS FOR RELATIVELY U-CONTINUOUS RANDOM OPERATORS WITH APPLICATIONS
Godwin Amechi Okeke 영남수학회 2017 East Asian mathematical journal Vol.33 No.3
It is our purpose in this paper to introduce the concept of best random proximity pair for subsets A and B of a separable Banach space E. We prove some best random approximation and best random proximity pair theorems of certain classes of random operators, which is the stochastic verse of the deterministic results of Eldred et al. [22], Eldred et al. [18] and Eldred and Veeramani [19]. Furthermore, our results generalize and extend recent results of Okeke and Abbas [42] and Okeke and Kim [43]. Moreover, we shall apply our results to study nonlinear stochastic integral equations of the Hammerstein type.
Godwin Kwame Ahiale,Doo-Hyun Kim,Won-Jon Yang,Jong-Hoon Lee,Yong-Jun Oh 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.4
We investigated the change of precipitation behavior and impact resistance as a function of depth from the surface of thickblock of SAF 2507 super duplex stainless steel with the thickness (T) of 200 mm after water quenching from 1050 °C. Theamount of detrimental sigma phase increased smoothly until the depth of 0.25T, followed by a rapid increase from 0.25T tothe center. However, the impact strength decreased signifi cantly with only 1.3% of area fraction of sigma phase as the depthincreased past 0.1T. Based on fractography analysis for the samples at such small depth ranges, the distance between thesigma phase particles aff ected the relative amount of initiating brittle cracks in front of the notch and was one of the crucialfactors that dramatically reduced impact resistance with depth.
Low-Cycle Fatigue Behavior of Reduced Activation Ferritic-Martensitic Steel at Elevated Temperatures
Godwin Kwame Ahiale,Won‑Doo Choi,Seungyon Cho,Yi‑Hyun Park,Young‑Bum Chun,Yong‑Jun Oh 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.1
Changes in the low-cycle fatigue (LCF) behavior of reduced activation ferritic-martensitic (RAFM) steel containing trace amount of Zr—namely, Advanced Reduced Activation Alloy (ARAA) were presented in the temperature range of 573 to 873 K. The fatigue lifetime decreased significantly as the temperature increased from 573 to 823 K, but it was rather similar between 823 and 873 K, where the tensile properties deteriorated most rapidly. The decrease in lifetime at elevated temperatures is mainly due to the disappearance of the initial tempered martensitic structure during cycling resulting in rapid cyclic softening and local oxidation at surface slip bands which led to earlier crack initiation. The fatigue lifetime and cyclic softening behavior of ARAA were compared with those of the other conventional RAFM steels.
Correlation between the Microstructure and Mechanical Properties of W-Bearing Ti-6Al-4V Alloys
Godwin Kwame Ahiale,계인석,권영삼,오용준 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.6
W-containing Ti-6Al-4V alloys (W=0, 1, and 5 wt%) were fabricated by the powder injection molding process, and the corresponding effects of tungsten content on the mechanical properties and microstructure of the alloys were investigated. The alloy powders were sintered at 1200 °C and then hot-isostatically-pressed at 900 °C. The fabricated alloys were subjected to microstructural and chemical analyses, and tensile and nano-indentation tests. The yield strength and tensile strength proportionally increased as the W content was increased from 0 wt% to 5 wt%. Ductility was not affected by the addition of up to 5 wt% W due to its complete dissolution in the matrix. Higher W addition induced finer α/β lamellar microstructures and increased the β to α phase ratio. Moreover, the added W dissolved preferentially in the β phase by solid solution hardening, increasing the hardness of the β phase, which originally was significantly softer than the α phase. For the alloys containing up to 5 wt% W, the strengthening without ductility loss was attributed to the finer α/β lamellae and the volume increase in the β phase hardened by W. These results suggest that adding W to Ti-6Al-4V alloy is a promising method for developing Ti alloys with both high strength and toughness.
The Determinants of Firm Performance and Bribery: Evidence from Manufacturing Firms in Nigeria
Godwin Okafor 한국국제경제학회 2017 International Economic Journal Vol.31 No.4
This paper uses ordinary least squares with firm effects and Probit regression models to investigate the determinants of firm performance and the likelihood of firms to pay bribes. Results for the manufacturing firms in Nigeria show that skilled workforce, exports, foreign ownership and capital investment influence firm performance. Conversely, poor electricity delivery and difficulty obtaining finance impede firm performance. Total sales and time spent dealing with government regulations increase the likelihood of firms to pay bribes. Surprisingly, foreign firms are as much likely to pay bribes as domestic firms. Policy implications from the findings are important considering that the manufacturing sector assumes an important role in the Lewis theory of economic development.