Numerical and Experimental Analysis of the Powder Flow Streams in the Laser Aided Material Deposition Process

Axial powder stream concentration between the nozzle end and the deposition point is an important process parameter in the laser aided material deposition process. The powder concentration is greatly influenced by the nozzle geometry in use. This paper describes the numerical and experimental analysis of this important parameter in relation to the coaxial nozzle. The experiments are performed with the different nozzle geometries to generate various flow patterns of the gravity fed powder in a cold stream. The results of the experimental analysis are compared with the numerical simulation and found justified. These results are used in concluding the significance of important nozzle parameters for various powder concentration modes.Mechanical Engineerin

Electron interactions with astro chemical compounds

In present work electron induced processes with important astro-compounds found in the tholins of Titan are investigated. We report calculated total elastic cross sections Qel, total inelastic cross sections Qinel, total ionization cross sections Qion, total excitation cross sections ∑Qexc and total cross sections QT for hydrogen cyanide (HCN), cyanoacetylene (HCCCN), vinyl cyanide (CH2CHCN), methanimine (CH2NH) and ethanimine (CH3CHNH) on electron impact for energies from ionization threshold to 5 keV. We have employed the Spherical Complex Optical Potential (SCOP) formalism to investigate elastic as well as inelastic processes and used Complex Scattering Potential – ionization contribution (CSP-ic) method to derive ionization cross sections. In absence of any theoretical or experimental data of ionization cross sections except for HCN and HCCCN, we have computed Qion using the Binary- Encounter- Bethe (BEB) method for all these molecules and have found reasonable agreement. This is the maiden attempt to report various total cross sections for all these astro-molecules except HCN and HCCCN

The Seventh Data Release of the Sloan Digital Sky Survey

This paper describes the Seventh Data Release of the Sloan Digital Sky Survey (SDSS), marking the completion of the original goals of the SDSS and the end of the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most of the roughly 2000 deg^2 increment over the previous data release lying in regions of low Galactic latitude. The catalog contains five-band photometry for 357 million distinct objects. The survey also includes repeat photometry over 250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A coaddition of these data goes roughly two magnitudes fainter than the main survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2 in the Northern Galactic Cap, closing the gap that was present in previous data releases. There are over 1.6 million spectra in total, including 930,000 galaxies, 120,000 quasars, and 460,000 stars. The data release includes improved stellar photometry at low Galactic latitude. The astrometry has all been recalibrated with the second version of the USNO CCD Astrograph Catalog (UCAC-2), reducing the rms statistical errors at the bright end to 45 milli-arcseconds per coordinate. A systematic error in bright galaxy photometr is less severe than previously reported for the majority of galaxies. Finally, we describe a series of improvements to the spectroscopic reductions, including better flat-fielding and improved wavelength calibration at the blue end, better processing of objects with extremely strong narrow emission lines, and an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor correction

Effects of nozzle geometry parameters on powder stream structure in laser aided deposition process

The Laser Aided Manufacturing Processes (LAMP) developed at the University of Missouri-Rolla is used to fabricate three dimensional metal and ceramic parts. The part material is supplied in the form of powder in the size of microns and the laser is used to melt the powder onto a substrate. The CAD model is basically converted to a format called STL files where the model is split into numerous triangles. This facilitates the slicing of the CAD model. Toolpath generation software is used to generate the deposition toolpath from the STL file. The laser scans the substrate and deposits the material according to the slices which solidifies and forms the final part near to net shape. The deposition process depends on various process parameters. One of the important parameter is powder flow structure and mass flow rate of the powder. The powder stream structure depends on the nozzle geometry in use. This thesis describes the influence of different nozzle geometry parameters on the powder flow mode. Thus various effects of nozzle parameters are analyzed over here. The different powder flow structures are studied in relation to achieve better efficiency of the process. The important issues addressed are outlined as follows: a) The analysis of the concentration structures formed by various nozzle geometry settings to relate their influence on the deposition process. b) The structure of the merging patterns of different powder streams in axial as well as radial directions. c) The randomization of experiments performed so that the data collected would be statistically valid --Abstract, page iv

Analysis of the Powder Flow Characteristics for the Direct Laser Deposition Process

Direct laser deposition process is one of the advanced technologies in the current industrial and research scenario. In this process, metal and/or alloy powder is directly fed into the melt pool created by the laser to form the solid parts. The powder flow characteristics play an important role in the laser aided deposition. The melting of the powder depends mostly on the laser beam spot size and the powder flow from the nozzle. The intention of this contribution is to study this basic parameter of the powder flow in detail with respect to the coaxial deposition nozzle. Different nozzle dimensions are used to analyze the different flow patterns of the gravity fed powder in a cold stream. Rapid prototyping technique is used to make this analysis cost and time efficient. This analysis lays down the benchmark for the coaxial nozzle design used for the laser aided deposition process in a productive manne

Numerical and Experimental Study of Shielding Gas Orientation Effects on Particle Stream Concentration Mode in Coaxial Laser Aided Material Deposition Process

Laser aided deposition quality largely depends on the powder stream structure below the nozzle. Modeling of the powder concentration distribution rarely relies on the numerical approach partially due to the complex phenomenon involved in the two-phase turbulence flow. In this paper, a numerical model is introduced to predict the particle-gas flow precisely and economically in order to meet the practical requirement for coaxial nozzle design optimizations. This model is able to quantitatively predict the powder stream concentration mode under different outer shielding gas directions and inner/outer gas velocity ratio. The numerical simulation results are compared with the experimental study using prototyped coaxial nozzles. The results are found to match. This study shows that the particle concentration mode is influenced significantly by the outer gas direction and gas flow settings

Theoretical electron impact total cross sections for tetrahydrofuran (C

We report electron impact total cross sections for tetrahydrofuran (C4H8O) from ionization threshold to 5 keV. We have employed Spherical Complex Optical Potential (SCOP) to calculate total cross sections QT, total inelastic cross sections Qinel and total elastic cross sections Qel and have used Complex Scattering Potential – ionization contribution (CSP-ic) formalisms to compute total ionization cross sections Qion and summed total excitation cross sections ∑ Qexc. We have compared our cross sections with available experimental as well as theoretical results and have found good agreement wherever available. This is the maiden attempt to report the total excitation cross sections for this target

Effect of Rasayana Ghana tablet (An Ayurvedic formulation) on improving quality of life of stressed individuals

Stress is the most hazardous factor which can adversely affect the quality of life. Ayurvedic Rasayana formulations can be used to relieve stress and there forth improve and maintain healthy quality of life. In the present study, the effect of a classical ayurvedic Rasayana formulation comprising three herbs Gokshura (Tribulus terrestris Linn.), Aamalaki (Emblica officinalis Gaertn.) and Guduchi (Tinospora cordifolia Miers.) is assessed on health, wellness and quality of life questionnaire in stress prone patients. Total 108 patients complaining of stress and decreased quality of life were randomly divided into two groups of Rasayana Ghana tablets (RGT) and Placebo group (PG). The drug was given in a dose of two tablets of 500mg twice a day with ghee and honey in unequal proportion. Result was assessed on the parameters given in quality of life questionnaire.  The data was then analyzed by applying Wilcoxon non parametric test in each group and chi-square test to compare efficacy in both groups. RGT seems to be effective in decreasing the physical complaints and improving mental/emotional state, adaptation to stress, life enjoyment and overall quality of life to a significant level in each sub scale