No abstract

Distinct, periodic arc-shaped ripples are observed on the surface of the weld bead in almost any welded components which have a significant effect on weld quality. This article presents the complex transport phenomena and their effect on the formation of ripples in three-dimensional moving gas metal arc welding. The transient distributions of the melt flow velocity and temperature in the weld pool, weld pool shape and dynamics, and solidified weld bead are calculated. It is found that the surface ripples are formed by the interplay between the up-and-down weld pool dynamics, caused mainly by the periodic droplet impingements, and the rate of weld pool solidification. The effects of various welding parameters, including the welding current, droplet size, droplet frequency, droplet impinging velocity, and travel speed on the pitch ͑distance between two ripples͒ and height of the ripple are investigated. This study provides fundamental understanding to the underlying physics that cause the formation of ripples with different pitches and heights.

No abstract

No abstract

No abstract

The 1014 nucleotides long gene-encoding beta-mannanase from Bacillus subtilis strain MA139 was cloned using PCR. To obtain high expression levels in Pichia pastoris, the beta-mannanase gene was optimized according to the codon usage bias of P. pastoris and fused downstream of GAP promoter. The reconstituted plasmid pGAP-mann was transformed into P. pastoris X-33 strain to constitutively express beta-mannanase. When cultured at 28 degrees Celsius for 3 days protein yields up to 2.7 mg/mL was obtained with the enzyme activity of up to 230 U/mL. In comparison, wild-type gene product yielded 1.9 mg/mL and 170 U/mL, respectively indicating that the protein yield and enzyme activity were significantly improved by codon modification. After purification, the enzyme properties were characterized. The optimal activity was at pH 6.0 and 50 degrees Celsius. In the pH range of 3.0 to 9.0, beta-mannanase showed above 60% of its peak activity. Among the numerous ions tested copper significantly inhibited the enzyme activity. These results suggested that codon-optimized beta-mannanase expressed in P. pastoris could potentially be used as an additive in the feed for monogastric animals.

No abstract

Three-dimensional modeling of transport phenomena and their effect on the formation of ripples in gas metal arc welding J. Appl. Phys. 107, 054905 (2010); 10.1063/1.3326163Effects of current on droplet generation and arc plasma in gas metal arc weldingThe effect of shielding gas composition on welding performance and weld properties in hybrid CO 2 laser-gas metal arc welding of carbon manganese steel Predictions of metal droplet formation in gas metal arc welding. II.This article presents the effects of shielding gas compositions on the transient transport phenomena, including the distributions of temperature, flow velocity, current density, and electromagnetic force in the arc and the metal, and arc pressure in gas metal arc welding of mild steel at a constant current input. The shielding gas considered includes pure argon, 75% Ar, 50% Ar, and 25% Ar with the balance of helium. It is found that the shielding gas composition has significant influences on the arc characteristics; droplet formation, detachment, transfer, and impingement onto the workpiece; and weld pool dynamics and weld bead profile. As helium increases in the shielding gas, the droplet size increases but the droplet detachment frequency decreases. For helium-rich gases, the current converges at the workpiece with a "ring" shape which produces non-Gaussian-like distributions of arc pressure and temperature along the workpiece surface. Detailed explanations to the physics of the very complex but interesting transport phenomena are given.