User's manual for RAVFAC - A radiation view factor digital computer program

Contour integrals and finite difference in Radiation View Digital Computer Progra

Radiation view factor program

Computer program, RAVFAC, calculates diffuse radiation view factors, using contour integrals. Technique is combined with finite difference /double summation/ technique to compose total program package

Modification to the shading routine in the HREC orbital drag coefficient computer program Final report

Shading and pre-shading techniques for modified orbital drag coefficient computer progra

Oligopeptide transport : cloning and characterization of a new gene family

Peptide transport is a widely observed phenomenon defined as the translocation of peptides 2-6 residues in length across the plasma membrane in an energy-dependent manner. Internalized peptides are rapidly hydrolyzed by peptidases, and the resulting amino acids are used for protein synthesis or alternatively as a source of nitrogen or carbon. Physiological evidence suggested that the pathogenic fungus Candida albicans has at least two different peptide transporters: a di-/tripeptide transporter named CaPtr2p and an oligopeptide transporter system which accomodates peptides of 3-5 residues. The purpose of this study was to 1) clone and characterize the gene(s) responsible for oligopeptide transporter in C. albicans and 2) explore the role of oligopeptide transport in virulence. Part II of this dissertation describes how the oligopeptide transport gene OPT1 was cloned from C. albicans. Using growth conditions under which Saccharomyces cerevisiae strain PB1X-9B does not transport tetra- and pentapeptides, we were able to identify OPT1 as a gene that allowed PB1X-9B to utilize tetra- and pentapeptides as a sole source of an auxotrophic supplement. OPT1 bestowed oligopeptide transport activity to PB1X-9B as measured by sensitivity to toxic oligopeptides and the ability to accumulate a radiolabled tetrapeptide. Part III of this dissertation details how we identified the OPT1 homolog isp4 from S. pombe and how subsequent characterization of a deletion strain revealed that isp4 encodes an oligopeptide transporter. Furthermore, based upon the four criteria of protein length, function, topology, and conserved functional domains, we proposed that OPT1 from C. albicans, isp4 from S. pombe, and YPR194C and YJL212C from S. cerevisiae comprise the first identified members of a novel family of transport proteins. Part IV of this dissertation summarizes the construction and characterization of several OPT1 disruptant strains. Analyses of the disruptants revealed that Opt1p is a high-affinity/low-capacity transporter and that another oligopeptide transport system exists in C. albicans. The role of OPT1 in one murine model of systemic candidiasis was explored and the possible roles for OPT1 in virulence are discussed

Pbf-lb process-induced regular cavities for lightweight alsi10mg structures

In powder bed fusion with laser beam (PBF-LB), two process-induced defects by pore formation are known: local spherical pores by the keyhole effect and geometrically undefined pores caused by lack of fusion. Both pore types are heterogeneously distributed and can be used for lightweight or damping design applications. The achievable porosity is limited to around 13%. This article presents a novel process-controlled method enabling the targeted and reproducible manufacturing of solid parts with regularly distributed cavities, currently up to 60% porosity in AlSi10Mg, using the balling effect. This eliminates the need for time-consuming digital pre-processing work

Influence of initial powder layer thickness and focus deviation on the properties of hybrid manufactured parts by Laser Powder Bed Fusion

In hybrid-additive manufacturing using powder bed fusion with laser beam (PBF-LB) conventionally manufactured base-bodies are overprinted with an individual geometry. In this paper, the influence of deviations of the initial layer thickness, and the focal plane on the component properties are investigated. For separate consideration of the individual effects, purely additive (AlSi10Mg) and hybrid-additive (AlSi10Mg on EN AW6082) test specimens were manufactured. The layer thickness was varied from 0 to 200 µm, and the focal plane between 0 and -8 mm. The influence on the microstructure due to the altered induced energy input is analyzed. These findings are correlated with respect to the tensile strength and material hardness. The highest strength is achieved with an initial layer thickness of 50 µm. A hardness decrease of 8 % due to hot stress cracks in the interface is avoided by targeted shifting of the focal plane

Optimization of the layer quality by TiC nanoparticles in the ultrasonic excited recoating process with non-spreadable AlSi10Mg matrix B4C particle-powder composites for powder bed based additive manufacturing

High-strength and stiffness materials can further increase the lightweight construction potential of additive manufacturing. One way to achieve this, is to produce particle-reinforced aluminum matrix composites (PAMCs). A significant increase in strength can be achieved with ceramic particles smaller than 6 μm and a volume fraction of 20 to 30 % in other metallurgical processes. Due to the larger interparticle forces compared to the gravitational force, such powder mixtures are not flowable and cannot be recoated in PBF-LB with static recoaters like rubber lips and metal blades. Two approaches were compared to solve this problem. Firstly, the new broadband ultrasonic excitation of the recoater metal combs and secondly, flow enhancing with nanoparticles. The influence of the approaches was investigated by image analysis of the recoated layers for defects in an SLM 280 HL 1.0. Broadband vibration enables reliable recoating of AlSi10Mg powders mixed with up to 20 vol% 6 μm boron carbide particles without layer defects. Combined with TiC nanoparticle coating, 25 vol% are possible. The solution can securely be operated in build jobs

Comparison of in-process laser drying with furnace and vacuum drying to reduce moisture of AlSi10Mg powder processed in Laser Powder Bed Fusion

In most powder bed-based laser melting systems (PBF-LB), metal powders must be handled without inertization but in an air atmosphere for a short time, increasing the AlSi10Mg powder moisture and reducing the achievable component density. Consequently, different drying methods were investigated. Drying in a furnace with an inert atmosphere, using a vacuum to evaporate the water at low temperatures, and vaporizing moisture layerwise from the spreaded powder with a defocused, low-power laser beam as a further process step of the PBF-LB process. Therefore, four different moisturized powders, which were dried with different settings for the drying methods, are analyzed. All drying methods reduce the moisture content of the powder, with in-process drying being the most effective. Due to the oxide layer growth around the particles during furnace and vacuum drying, the achievable sample density after drying is worse. In-process drying with low energy density is the best option to reach a reduction of hydrogen pores and an increase of density