5,016 research outputs found
Effect of Electro-Magnetic Stirring in Mold on the Reduction of Subsurface Defect and Macro segregation in CC Billets
No full textCrystal structure of Delta(5)-3-ketosteroid isomerase from Pseudomonas testosteroni in complex with equilenin settles the correct hydrogen bonding scheme for transition state stabilization
No full textDelta(5)-3-Ketosteroid isomerase from Pseudomonas testosteroni has been intensively studied as a prototype to understand an enzyme-catalyzed allylic isomerization, Asp(38) (PKalpha similar to 4.7) was identified as the general base abstracting the steroid C4 beta proton (pK(alpha) similar to 12.7) to form a dienolate intermediate. A key and common enigmatic issue involved in the proton abstraction is the question of how the energy required for the unfavorable proton transfer can be provided at the active site of the enzyme and/or how the thermodynamic barrier can be drastically reduced. Answering this question has been hindered by the existence of two differently proposed enzyme reaction mechanisms. The 2.26 Angstrom crystal structure of the enzyme in complex with a reaction intermediate analogue equilenin reveals clearly that both the Tyr(1.4) OH and Asp(99) COOH provide direct hydrogen bonds to the oxyanion of equilenin, The result negates the catalytic dyad mechanism in which Asp(99) donates the hydrogen bond to Tyr(14), which in turn is hydrogen bonded to the steroid. A theoretical calculation also favors the doubly hydrogen-bonded system over the dyad system. Proton nuclear magnetic resonance analyses of several mutant enzymes indicate that the Tyr(14) OH forms a low barrier hydrogen bond with the dienolic oxyanion of the intermediate.X1174sciescopu
Development of multi-component DeNOx catalyst by newly constructed combinatorial evaluation system, SUPER-I
No full textApplication of chemiluminescence NOx analyzer as a high-throughput screening tool in selective catalytic reduction of NOx
No full textDesign of radar absorbing structures using glass/epoxy composite containing carbon black in X-band frequency ranges
No full textIt is an important issue not only for military purposes but also from commercial point of view, whether or not the reflective wave from an incident electromagnetic wave can be nullified. In this research, by blending conductive carbon black with the binder matrix of glass/epoxy composite, a radar absorbing structure (RAS) which can support loads and absorb the electromagnetic wave has been designed. The RAS was specially designed so as to exhibit the optimum absorptivity for X-band of (8.2-12 GHz) frequency ranges, centered at 10 GHz. Its absorbing characteristics were also investigated. Unlike other existing measurements of reflection loss using a waveguide, the reflection loss within an anechoic chamber simulating the radar cross section method of measurement was used with a plane-wave shaped incident wave. An optimized multi-layer design of RAS using the adopted material system is described in this research
An efficient postbuckling analysis technique for composite stiffened curved panels
No full textSeveral efficient techniques are presented for the postbuckling analysis of composite stiffened structures in this paper. Some aerospace structures allow local buckling in order to increase structural efficiency. This idea may be a very effective design concept, but it takes a great deal of time in structural design. Due to its geometrical and material nonlinearity, the postbuckling analysis process requires a long computational time. fit this report, to reduce the computational time, efficient analysis techniques are proposed. A change in the element type used, separation of the linear response region, and the termination of the analysis after ultimate failure of the structure were applied to the analysis. As a result. about 80% of the computational time was reduced with high accuracy
Electromagnetic characteristics of frequency selective fabric composites
No full textFrequency selective fabric composites that transmit microwaves in certain frequency bands are proposed. The composites consist of carbon fibres and low-loss dielectric fibres that together build periodic patterns. Unlike existing metallic frequency selective surfaces, the frequency selective fabric composite with additional load-carrying capability showed an amount of transmission near a resonance frequency
Fatigue life modeling of short fiber reinforced metal matrix composites using mechanical and acoustic emission responses
No full textThe cyclic fatigue behavior of short fiber reinforced metal matrix composites was studied. Three fatigue life prediction models were developed by monitoring the resultant maximum strain and counts of acoustic emission during cyclic fatigue. Their increasing trends with the number of fatigue cycles were studied using the assumption that they can be expressed as a power-law function of the fatigue cycle number. Post-fatigue static tension tests were conducted to examine the degradation of the damaged materials. The acoustic emission count accumulated during tension testing decreased as the applied fatigue cycles increased; this change was also used to formulate life prediction models. All the new models show a better agreement to experimental data than do the existing equations.X1111sciescopu
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