Modeling of laser keyhole welding: Part I. mathematical modeling,numerical methodology,role of recoil pressure,multiple reflections,and free surface evolution

A three-dimensional laser-keyhole welding model is developed, featuring the self-consistent evolution of the liquid/vapor (L/V) interface together with full simulation of fluid flow and heat transfer. Important interfacial phenomena, such as free surface evolution, evaporation, kinetic Knudsen layer, homogeneous boiling, and multiple reflections, are considered and applied to the model. The level set approach is adopted to incorporate the L/V interface boundary conditions in the Navier-Stokes equation and energy equation. Both thermocapillary force and recoil pressure, which are the major driving forces for the melt flow, are incorporated in the formulation. For melting and solidification processes at the solid/liquid (S/L) interface, the mixture continuum model has been employed. The article consists of two parts. This article (Part I) presents the model formulation and discusses the effects of evaporation, free surface evolution, and multiple reflections on a steady molten pool to demonstrate the relevance of these interfacial phenomena. The results of the full keyhole simulation and the experimental verification will be provided in the companion article (Part II).     

A novel discrete control strategy for independent stabilization of parallel three-phase boost converters by combining space-vector modulation with variable-structure control

We propose a discrete nonlinear controller, developed in a synchronous frame, for a parallel three-phase boost converter consisting of two modules. The basic idea, however, can be extended to a system with N modules. Each of the closed-loop power-converter modules operates asynchronously without any communication with the other modules. The controller stabilizes the currents on the dq-axes and limits the flow of the pure-zero sequence current. It combines the space-vector modulation scheme with a variable-structure control, thereby keeping the switching frequency constant and achieving satisfactory dynamic performance.     

Coprocessor design for multilayer surface-mounted PCB routing

The authors present the issues involved in the design of a special-purpose processing array system, called HAM, which accelerates computationally intensive wire routing tasks. It is especially suited for double-sided surface-mounted boards, which require complex three-dimensional search operations over multiple wiring planes. The novel features of the design include a hexagonal interconnection scheme to improve workload distributions during multilayer concurrent search operations and the VLSI custom design of the processors. Particular emphasis has been placed on the demands of maze routing. A cell-address propagation scheme, which is quite different from the traditional grid-coordinate approach, is discussed. It provides rapid lookup of pertinent routing information and can be extended to any distributed memory multiprocessor system. A global pipelining scheme of cell updates and expands is discussed. Experimental results are presented relating the speedup to various criteria for two different modes of parallel wave propagation     

UV-shielding by a polyurethane/f-Oil fly ash-CeO2 protective coating

A waste material called oil fly ash (OFA) was acid-functionalized, yielding f-OFA-COOH, which was then reacted with cerium oxide (CeO₂) to make CeO₂-functionalized OFA, or f-OFA-CeO₂. Pristine OFA and f-OFA-CeO₂ were used to make waterborne polyurethane (WBPU) dispersions, referred to as WBPU/OFA and WBPU/f-OFA-CeO₂, respectively, with defined OFA and f-OFA-CeO₂ content. All the dispersions were applied to mild steel as organic coatings to evaluate their protective properties, such as their hydrophobicity, adhesive strength and UV-shielding resistance. These protective properties varied based on the OFA and f-OFA-CeO₂ content. The highest water contact angle, minimum water swelling and maximum adhesive strength were found using WBPU/f-OFA-CeO₂-20 coating (using 2.00 wt% f-OFA-CeO₂), which also showed the maximum ultraviolet (UV) absorption via UV–vis spectroscopy analysis. This UV shielding result also matched field test results, as that coating was found to exhibit the lowest UV degradation near a marine atmosphere, as shown by X-ray photoelectron spectroscopy (XPS) analysis. The least affected hydrophobicity was also recorded for the sample with the WBPU/f-OFA-CeO₂-20 coating.     

Long Duration Persistent Photocurrent in 3 nm Thin Doped Indium Oxide for Integrated Light Sensing and In-Sensor Neuromorphic Computation

Miniaturization and energy consumption by computational systems remain major challenges to address. Optoelectronics based synaptic and light sensing provide an exciting platform for neuromorphic processing and vision applications offering several advantages. It is highly desirable to achieve single-element image sensors that allow reception of information and execution of in-memory computing processes while maintaining memory for much longer durations without the need for frequent electrical or optical rehearsals. In this work, ultra-thin (<3 nm) doped indium oxide (In₂O₃) layers are engineered to demonstrate a monolithic two-terminal ultraviolet (UV) sensing and processing system with long optical state retention operating at 50 mV. This endows features of several conductance states within the persistent photocurrent window that are harnessed to show learning capabilities and significantly reduce the number of rehearsals. The atomically thin sheets are implemented as a focal plane array (FPA) for UV spectrum based proof-of-concept vision system capable of pattern recognition and memorization required for imaging and detection applications. This integrated light sensing and memory system is deployed to illustrate capabilities for real-time, in-sensor memorization, and recognition tasks. This study provides an important template to engineer miniaturized and low operating voltage neuromorphic platforms across the light spectrum based on application demand.     

Erratum to: Laser-Aided Direct Writing of Nickel-Based Single-Crystal Super Alloy (N5)

Metallurgical and Materials Transactions A -     

Hydrodynamic dispersion of reactive solute in a Hagen-Poiseuille flow of a layered liquid

An analysis of the solute dispersion in the liquid flowing through a pipe by means of Aris-Barton's ⒈method of moments',under the joint effect of some finite yield stress and irreversible absorption into the wall is presented in this paper.The liquid is considered as a three-layer liquid where the center region is Casson liquid surrounded by Newtonian liquid layer.A significant change from previous modelling exercises in the study of hydrodynamic dispersion,different molecular diffusivity has been considered for the different region yet to be constant.For all time period,finite difference implicit scheme has been adopted to solve the integral moment equation arising from the unsteady convective diffusion equation.The purpose of the study is to find the dependency of solute transport coefficients on absorption parameter,yield stress,viscosity ratio,peripheral layer variation and in addition with various diffusivity coefficients in different liquid layers.This kind of study may be useful for understanding the dispersion process in the blood flow analysis.     

Synthesis of a terpolymer and a tetrapolymer using monomers of diallylamine salts and SO<Subscript>2</Subscript> and their application as antiscalants

An aqueous solution of diallylammonium salts (CH₂ = CHCH₂)₂NH⁺(CH₂)₃A^? having A^? as: CO₂ ^? (I), PO₃H₂ Cl^? (II) and SO₃ ^? (III) in 1:1:1 mol ratio underwent ammonium persulfate-initiated ter cyclopolymerization to yield pH-responsive zwitterionic polymer IV with random placements of the monomers in the same ratio. During dialysis, PO₃H₂Cl^? of the incorporated monomer units of II upon depletion of HCl became PO₃H^?. Likewise, azobisisobutyronitrile-initiated cyclopolymerization of I, II, III, and SO₂ in a mole ratio of 1:1:1:3 provided pH-responsive tetrapolymer V in over 90 % yield with random and alternative placements of I–III and SO₂ units, respectively, in the same ratio as the feed. Polyzwitterions (PZs) IV and V were insoluble in salt-free water but soluble in the presence of salts. The critical salt concentrations required to promote water solubility of PZ IV were determined to be 0.356 M NaCl, 0.237 M NaBr and 0.128 M NaI, whereas for PZ V the corresponding values were found to be 2.25, 1.26 and 0.862 M, respectively. PZs IV and V were converted into anionic polyelectrolytes VI and VII upon basification with NaOH. The viscosity and antiscalant behaviors of VI and VII were examined. The polymers demonstrated remarkable scale inhibition efficacies; at a dose of 10 ppm, both IV (+NaOH) and V (+NaOH) delayed the precipitation of CaSO₄ from its supersaturated solution up to 920 and over 4000 min, respectively. For a small concentration of 5 ppm of polymer V, a scale inhibition of 100 % over 100 min verified it to be a potential effective antiscalant additive in reverse osmosis plants.     

Characterization of tribocharging properties of powder paint

The charge-to-mass ratio (q/m) of individual particles plays a vital role in the powder coating process. Simultaneous measurements of particle size and electrostatic charge were performed on triboelectrically charged powder paint and other powders in the particle size range 1.0 to 65.0 μm in diameter. An electrical single particle aerodynamic relaxation time (ESPART) analyzer was used to measure electrostatic charge (q) and aerodynamic size (d_a) distributions on a single particle basis and in a noninvasive manner. The powders were triboelectrically charged against nonconducting surfaces. Experimental data show that (1) the magnitude of the charge increases linearly with the surface area of the particle and consequently, the charge-to-mass ratio of the particles decreases inversely with respect to d_a in the entire size range, and (2) twenty to sixty percent of the particles were charged with opposite polarity. The average charge attained by particles larger than 4.0 μm in diameter was less than the Gaussian limit of saturation charge. The charge-to-mass ratio of the bulk powder sample depends upon the range of particle size in the sample. The mass median aerodynamic diameter of the sample studied was 30.0 μm with the geometric standard deviation of 2.0