Collision-based Model Research Articles

Low energy femtosecond pulsed laser ablation of Nd:YAG laser crystal in high-pressure oxygen and nitrogen background gas

A low-energy femtosecond (fs) pulsed laser was utilized to ablate the Nd:YAG laser crystal target in high-pressure oxygen (O2) and nitrogen (N2) background gases. Only minute amounts of neodymium (Nd), yttrium (Y), and aluminum (Al) were detected in the deposited material due to the thermalization resulting from low laser pulse energy and significant scattering caused by the high background gas pressure. We used a collision-based model and peak-fitting method of the angular distribution of the plume to explain the result. The collision-based model was used to explain and determine the probability distribution of the elements arriving from the target to the substrate. The magnitude of the probability distribution obtained with O2 background gas is higher as compared to N2 background gas owing to the former’s higher collision frequency. The peak-fitting method of the angular distribution of Nd, Y, and Al provided better approximations of the ratio of atoms arriving after ablation as compared to the collision-based model. Further improvements can be carried out to better predict the deposited material ratio.

Powder particle–wall collision-based design of the discrete axial nozzle-exit shape in direct laser deposition

To improve the efficiency of the direct laser deposition (DLD) of metal powders, a concentrated powder-stream distribution is required, which can be affected by the shape of the powder-delivery nozzle. In this study, a simplified, powder particle–wall collision-based 3D numerical model of the powder flow in the nozzle was used to simulate the influences of the nozzle-exit shape on the concentration of the powder stream distribution, characterized by its diameter. The nozzle-exit shape was parametrized by the exit-cone angle, length, and inner-surface roughness. Based on the simulation results, the nozzle-exit shapes of three exit-cone angles (0°, 3.5° and 7.2°), various lengths and surface-roughness values were designed. For the two larger particle sizes of 22 μm and 82 μm considered, the wall-collision-dominated regime and the influence of the nozzle-exit shape were experimentally confirmed. In particular, a significant decrease in the powder-stream diameter when increasing the divergent nozzle-exit cone angle or decreasing its surface roughness and the nonlinear influence of the cone length were shown. Using single-layer, powder-deposition experiments it was demonstrated that by modifying the design of the nozzle-exit shape, the powder-catchment efficiency was increased by 13% due to the increased nozzle-exit cone angle and by 19% due to the reduced surface roughness. • Particle-wall collision-based model of powder flow in nozzle-exit was formulated. • Conical exit influence on powder stream was shown numerically and experimentally. • Increase of divergent nozzle-exit cone angle decreases powder stream diameter. • The nozzle-exit cone length nonlinearly influences the powder stream diameter. • Reducing the nozzle-exit cone roughness decreases the powder stream diameter.

The Elliptic Integral Machine: A Collision-based Model of Computation

In this work we will show how any elliptic integral can be computed by analyzing the asymptotic behavior of idealized mechanical models. Specifically, our results reveal how a set of circular billiard systems computes the canonical set of three elliptic integrals defined by Legendre. We will treat these Newtonian systems as a particular application of the billiard-ball model, a ballistic computer idealized by Eduard Fredkin and Tommaso Toffoli. Initially, we showed how to define the initial conditions in order to encode the computation of a set of integral functions. We then combined our first conclusions with results established in the 18th and 19th centuries mostly by Euler, Lagrange, Legendre and Gauss in developing the theory of integral functions. In this way, we derived collision-based methods to compute elementary functions, integrals functions and mathematical constants. In particular, from the Legendre identity for elliptic integrals, we were able to define a new collision-based method to compute the number $\pi$, while an identity demonstrated by Gauss revealed a new method to compute the arithmetic-geometric mean. In order to explore the computational potential of the model, we admitted a hypothetical device that measures the total number of collisions between the balls and the boundary. There is even the possibility that the methods we are about to describe could one day be experimentally applied using optical phenomena, as recent studies indicate that it is possible to implement collision-based computation with solitons.

Implications of non-Markovian quantum dynamics for the Landauer bound

We study the dynamics of a spin-1/2 particle interacting with a multi-spin environment, modelling the corresponding open system dynamics through a collision-based model. The environmental particles are prepared in individual thermal states, and we investigate the effects of a distribution of temperatures across the spin environment on the evolution of the system, particularly how thermalisation in the long-time limit is affected. We study the phenomenology of the heat exchange between system and environment and consider the information-to-energy conversion process, induced by the system–environment interaction and embodied by the Landauer principle. Furthermore, by considering an interacting-particles environment, we tune the dynamics of the system from an explicit Markovian evolution up to a strongly non-Markovian one, investigating the connections between non-Markovianity, the establishment of system–environment correlations, and the breakdown of the validity of Landauer principle.

Characterization of Force Deflection Properties for Vehicular Bumper-to-Bumper Interactions

This is the complete manuscript and replacement for SAE paper 2014-01-0482, which was retracted due to incomplete content. This paper reports on 76 quasi-static tests conducted to investigate the behavior of road vehicle bumper systems. The tests are a quasi-static replication of real world low speed collisions. The tests represented front to rear impacts between various vehicles. Force and deflection were captured in order to quantify the stiffness characteristics of the bumper-tobumper system. A specialized test apparatus was constructed to position and load bumper systems into each other. The purpose was to replicate or exceed damage that occurred in actual collisions. The fixture is capable of positioning the bumpers in various orientations and generates forces up to 50 kips. Various bumper-to-bumper alignments were tested including full overlap, lateral offset, and override/underride configurations. Force and displacement were recorded and the data was analyzed to develop system stiffness and crush parameters. These parameters can be used in a collision-based model to calculate vehicle delta-v (ΔV) and acceleration. The simulation uses an impact mechanics-based numerical algorithm published by Scott [6]. The paper reports on the test results of various combinations of vehicle categories. Vehicle type includes passenger, light transport and heavy vehicle bumper systems. Language: en

Magnetically ultraresponsive nanoscavengers for next-generation water purification systems

The development of sustainable, robust and energy efficient water purification technology is still challenging. Although use of nanoparticles is promising, methods are needed for their efficient recovery post treatment. Here we address this issue by fabrication of magnetically ultraresponsive 'nanoscavengers', nanoparticles containing synthetic antiferromagnetic core layers and functional capping layers. When dispersed in water, the nanoscavengers efficiently interact with contaminants to remove them from the water. They are then quickly collected (<5 min) with a permanent magnet, owing to their magnetically ultraresponsive core layers. Specifically, we demonstrate fabrication and deployment of Ag-capped nanoscavengers for disinfection followed by application of an external magnetic field for separation. We also develop and validate a collision-based model for pathogen inactivation, and propose a cyclical water purification scheme in which nanoscavengers are recovered and recycled for contaminant removal.

A collision-based model of spiral phyllotaxis

A collision-based model of spiral phyllotaxis