Indian Institute of Technology Guwahati

About: Indian Institute of Technology Guwahati is a education organization based out in Guwahati, Assam, India. It is known for research contribution in the topics: Catalysis & Computer science. The organization has 6933 authors who have published 17102 publications receiving 257351 citations.

A comprehensive review of the methods and mechanisms for powder feedstock handling in directed energy deposition

Abstract: Directed Energy Deposition (DED) is a subset of Metal Additive Manufacturing (MAM) technology with applications not just in part fabrication but also in surface cladding and part restoration The process uses a focused heat source to create a melt pool into which a feedstock material is injected, thereby, increasing the mass and volume of the melt pool Through synchronization, achieved via a CNC machine tool or a robotic arm, between the motion of the heat source, feedstock delivery, and the substrate complex parts can be fabricated layer-by-layer Metering, conveyance, and delivery of powder from feedstock reservoir to melt pool play an essential role in part quality and process efficiency Conventionally these tasks are carried out by pneumatic methods; however, several alternatives exist This article isolates feedstock handling in DED and presents an overview of key technologies that are used Several types of powder feed nozzles, along with their advantages and limitations, are briefly outlined Almost all commercially available DED units adopt the use of inert carrier gas for powder feedstock handling However, a few novel ideas that can serve as possible alternatives to this widely accepted pneumatic method are presented here Also, some of these mechanisms for powder handling, outlined in the context of DED, can be extended for other MAM processes such as Dry Powder Printing (DPP) and Selective Powder Deposition (SPD) Through highlighting key considerations that are pertinent to feedstock handling, the article aims to provide a guide for designing or procuring new setups that best suit the application A thorough understanding of existing technologies for feedstock handling in DED can help in innovating new ones to provide creative solutions to the problems faced by the current ones

Searches for rare or forbidden semileptonic charm decays

Abstract: We present searches for rare or forbidden charm decays of the form $X_c^+\to h^\pm\ell^\mp\ell^{(\prime)+}$, where $X_c^+$ is a charm hadron ($D^+$, $D^+_s$, or $\Lambda_c^+$), $h^\pm$ is a pion, kaon, or proton, and $\ell^{(\prime)\pm}$ is an electron or muon. The analysis is based on $384 fb^{-1}$ of $e^+e^-$ annihilation data collected at or close to the $\Upsilon(4S)$ resonance with the BaBar detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the 35 decay modes that are investigated. We establish 90% confidence-level upper limits on the branching fractions between $1 \times 10^{-6}$ and $44 \times 10^{-6}$ depending on the channel. In most cases, these results represent either the first limits or significant improvements on existing limits for the decay modes studied.