Individual Collisions Research Articles

Early stages of the mechanical alloying of TiC–TiN powder mixtures

The present work focuses on the alloying behavior of TiC–TiN powder mixtures submitted to mechanical processing by ball milling. Accurate X-ray diffraction analyses indicate a progressive modification of the unit cell parameters of the TiC and TiN phases, suggesting the formation of TiC- and TiN-rich solid solutions with an increasingly larger content of solutes. Once the discrete character of the mechanical treatment is taken into due account, the smooth change of the unit cell parameters can be explained by a sequence of mutual dissolution stages related to individual collisions. At each collision, the average chemical composition of small amounts of TiC- and TiN-rich phases changes discontinuously. The discontinuous changes can be tentatively ascribed to local mass transport processes activated by the mechanical deformation of powders at collisions.

Estimation of the mass of powder trapped at collision during ball milling from the kinetics of the mechanically activated decomposition of Ag oxalate

The present work aims at providing a direct experimental estimate of the amount of powder trapped at each collision during the mechanical processing by ball milling. Attention has been focused on the mechanochemical reactivity of anhydrous Ag oxalate powders, prepared by mixing Ag nitrate and Na oxalate aqueous solutions, and then filtering and drying the white precipitate formed. Suitable amounts of such powders were mechanically processed with a single milling ball. The mechanical processing induced the gradual decomposition of Ag oxalate into Ag and carbon dioxide. The process was followed by gravimetric analyses, and its kinetics related to individual collisions. It is shown that the decomposition process follows a simple exponential kinetics, which allows the identification and evaluation of an apparent rate constant. This can be regarded as a measure of the amount of powder trapped at each collision, which is roughly equal to 0.41 mg.

Structural responses of quasi-two-dimensional colloidal fluids to excitations elicited by nonequilibrium perturbations

We investigate the response of a dense monodisperse quasi-two-dimensional colloid suspension when a particle is dragged by a constant velocity optical trap. Consistent with microrheological studies of other geometries, the perturbation induces a leading density wave and trailing wake. We also use a hybrid version of Stokesian dynamics simulations to parse direct colloid-colloid and hydrodynamic interactions. We go on to analyze the underlying individual particle-particle collisions in the experimental images. The displacements of particles occur in chains reminiscent of stress propagation in sheared granular materials. From these data, we can reconstruct steady-state dipolar-like flow patterns that were predicted for dilute suspensions and previously observed in granular analogs to our system. The decay of this field differs, however, from point Stokeslet calculations, indicating that the nonzero size of the colloids is important. Moreover, there is a pronounced angular dependence that corresponds to the surrounding colloid structure, which develops in response to the perturbation. Put together, our results show that the response of the complex fluid is highly anisotropic owing to the fact that the effects of the perturbation propagate through the structured medium via chains of colloid-colloid collisions.

DNA Analysis by Application of Pt Nanoparticle Electrochemical Amplification with Single Label Response

This study demonstrates a highly sensitive sensing scheme for the detection of low concentrations of DNA, in principle down to the single biomolecule level. The previously developed technique of electrochemical current amplification for detection of single nanoparticle (NP) collisions at an ultramicroelectrode (UME) has been employed to determine DNA. The Pt NP/Au UME/hydrazine oxidation reaction was employed, and individual NP collision events were monitored. The Pt NP was modified with a 20-base oligonucleotide with a C6 spacer thiol (detection probe), and the Au UME was modified with a 16-base oligonucleotide with a C6 spacer thiol (capture probe). The presence of a target oligonucleotide (31 base) that hybridized with both capture and detection probes brought a Pt NP on the electrode surface, where the resulting electrochemical oxidation of hydrazine resulted in a current response.

Development and Validation of a Crash Culpability Scoring Tool

Objective: Several traffic safety research techniques require researchers to separate crash-involved drivers into culpable and nonculpable. Nonculpable drivers are assumed to be randomly involved in crashes by external factors and to approximate a noncollision control population. If this is true, factors that increase crash risk should be found more often in culpable than in nonculpable drivers. Though a culpability scoring tool has been developed for research purposes, that tool does not adequately address winter driving conditions (Robertson and Drummer 1994). Moreover, traditional culpability scoring requires assessors to read and score individual collision reports. The purpose of this study is to develop and validate an automated, rule-based Canadian culpability scoring tool that is capable of rapidly scoring police crash reports from large administrative datasets. Methods: We used an iterative approach to develop and validate our tool. First, the Robertson-Drummer culpability scoring tool was modified to include the extensive police report data collected in the British Columbia Traffic Accident System (TAS) and to account for winter driving conditions. This was done in consultation with traffic safety experts. The scoring tool was automated, employing a rule-based decision model that avoids interpretation of free-text reports. The scoring tool was applied to 73 collisions (134 drivers). Two experts also reviewed these collisions and determined the culpability of each driver. Discrepant cases were discussed to understand why the scoring tool differed from the expert assessment and the scoring tool was modified accordingly. The final tool was compared with expert assessment on another sample of 96 crashes. The tool was also applied to a sample of 2086 crash-involved drivers with known blood alcohol concentrations (BACs) and the adjusted odds of culpability were calculated for several BAC ranges. Results: The final scoring tool included 7 factors and had content validity for traffic safety experts. It had excellent agreement with expert scoring on the first set of collisions (kappa = 0.83, 95% confidence interval [CI]: 0.75–0.91) and on the second set (kappa = 0.84, 95% CI: 0.77–0.92). When applied to crash-involved drivers with known BAC levels, the scoring tool exhibited predictive validity: the odds of culpability increased with higher BACs, consistent with the known dose effect of BAC on crash risk. Conclusions: We have developed an automated culpability scoring tool contextualized to Canadian driving conditions. This tool will allow road safety researchers to assess collision responsibility in large administrative data sets derived from police reports.

Mechanical processing of Fe powders

Fe powders were mechanically processed by ball milling. The average size of coherent diffraction domains and the average strain content were determined by X-ray diffraction. A mathematical model was developed to describe the microstructural refinement process as a function of the number of collisions and to estimate the amount of powder effectively processed at individual collisions. The density of dislocations was also estimated. The obtained values suggest that Fe powders can locally undergo extremely severe deformation conditions.

Formation of a Al50Fe50 solid solution by mechanical alloying

This work investigates the alloying reaction undergone by Al50Fe50 powder mixtures submitted to mechanical processing by ball milling. The transformation kinetics was studied by quantitative X-ray diffraction. Experimental evidences indicate that Al gradually dissolves in Fe, finally forming a crystalline solid solution. A phenomenological model was developed to describe the observed kinetics with reference to the number of collisions and to the fraction of powder effectively processed at individual collisions. It is shown that only about 5μg of powders are involved in the Al dissolution processes at collision. It is also shown that a Al30Fe70 solid solution already forms at the first impact via local dissolution processes.

Deformation conditions for Ni powders undergoing mechanical processing

Ni powders were submitted to mechanical processing by ball milling. The microstructural refinement of the processed powders was followed by X-ray diffraction by evaluating the average crystallite size and the average strain content. The Vickers micro-hardness was also measured. The experimental evidences were rationalized using a phenomenological model, which allowed to estimate the amount of powder processed at individual collisions. The density of dislocations was also estimated and correlated with the experimental Vickers micro-hardness values. The connection between the work- and gain-hardening mechanisms described by the Bailey–Hirsch and Hall–Petch relationships is discussed.

Model of individual collisions for description of electron transport in matter

Distributions of electron characteristics are constructed with the use of data of elastic and nonelastic processes of interaction between electrons and matter. The data are taken from the National Nuclear Data Center, http://www.nndc.bnl.gov/. These characteristics are used for developing the technique of modeling the electron transport in matter. The developed model does not use the well-known slowdown approximation and multiple scattering theories. The comparison of some moments of the distributions with the NIST data is carried out. The satisfactory fit of some results computed by using the developed model and MCNP results is obtained.

Force driven separation of drops by deterministic lateral displacement

We investigate the separation of drops in force-driven deterministic lateral displacement (f-DLD), a promising high-throughput continuous separation method in microfluidics. We perform scaled-up macroscopic experiments in which drops settle through a square array of cylindrical obstacles. These experiments demonstrate the separation capabilities-and provide insight for the design-of f-DLD for drops of multiple sizes, including drops that are larger than the gaps between cylinders and exhibit substantial deformation as they move through the array. We show that for any orientation of the driving force relative to the array of obstacles, the trajectories of the drops follow selected locking directions in the lattice. We also found that a simple collision model accurately describes the average migration angles of the drops for the entire range of sizes investigated here, and for all forcing directions. In addition, we found a difference of approximately 20° between the critical angles at which the smallest and largest drops first move across a line of obstacles (column) in the array, a promising result in terms of potential size resolution of this method. Finally, we demonstrate that a single line of cylindrical obstacles rotated with respect to the driving force is capable of performing binary separations. The critical angles obtained in such single line experiments, moreover, agree with those obtained using the full array, thus validating the assumption in which the trajectory (and average migration angle) of the drops is calculated from individual obstacle-drop collisions.

Beam fragmentation in heavy ion collisions with realistically correlated nuclear configurations

We develop a new approach to production of the spectator nucleons in the ultrarelativistic heavy ion collisions. The energy transfer to the spectator system is calculated using the Monte Carlo based on the updated version of our generator of configurations in colliding nuclei which includes a realistic account of short-range correlations in nuclei. The transferred energy distributions are calculated within the framework of the Glauber multiple-scattering theory, taking into account all individual inelastic and elastic collisions using an independent realistic calculation of the potential energy contribution of each of the nucleon-nucleon pairs to the total potential. We show that the dominant mechanism of the energy transfer is tearing apart pairs of nucleons with the major contribution coming from the short-range correlations. We calculate the momentum distribution of the directed flow of emitted nucleons which is strongly affected by short-range correlations, including its dependence on the azimuthal angle. In particular, we predict a strong angular asymmetry along the direction of the impact parameter $\text{b}$, providing a unique opportunity to determine the direction of $\text{b}$. Also, we predict a strong dependence of the shape of the nucleon momentum distribution on the centrality of the nucleus-nucleus collision.

Three-dimensional cooling and detection of a nanosphere with a single cavity

We propose an experimental scheme to cool and measure the three-dimensional (3D) motion of an optically trapped nanosphere in a cavity. Driven by three lasers on TEM00, TEM01, and TEM10 modes, a single cavity can cool a trapped nanosphere to the quantum ground states in all three dimensions under the resolved-sideband condition. Our scheme can also detect an individual collision between a single molecule and a cooled nanosphere efficiently. Such an ability can be used to measure the mass of molecules and the surface temperature of the nanosphere. We also discuss the heating induced by the intensity fluctuation, the pointing instability, and the phase noise of lasers, and justify the feasibility of our scheme under current experimental conditions.

A few details of the austenite to martensite phase transformation in 304 stainless steel powders under mechanical processing

This work investigates the phase transformation kinetics of 304 stainless steel powders submitted to mechanical processing by ball milling. The mechanical treatment induces an austenite to martensite phase transformation at rates dependent on the frequency of collisions between the milling tools. The degree of phase transformation was estimated by quantitative X-ray diffraction as well as by saturation magnetization measurements, the martensite phase being ferromagnetic. A mathematical description of the phase transformation kinetics was developed by taking into account the intrinsic statistical character of the mechanical processing methods. This allowed us to obtain information on events occurring during individual collisions.

Vibration sensor for particle concentration measurement in pneumatic pipeline flows

Accurate measurements of pneumatically driven particle mass flow rate and particle size are necessary in order to maintain optimal combustion efficiency in coal-fired power plants and cement manufacturing facilities, as well as numerous other operations which are fed by multiple particle injection ports. Existing sensors for pneumatic particle concentration, such as concentration sensors, are typically prohibitively expensive and their measurements are sensitive to particle moisture content. A new sensor was developed for particle concentration measurement in pneumatic pipeline flow based on measurement of particle effects on fluid-induced oscillations of a probe extending into the flow. Since fluid-induced oscillations occur at a much lower frequency than do particle collisions, the measurements can be made with much simpler and less expensive equipment than is the case with impact sensors that attempt to resolve individual particle collisions. Experimental tests indicate three statistical measures of the probe acceleration data that exhibit smooth variation with the particle diameter and concentration data. The experimental data are used to train a neural net, which serves to interpolate the data. It is found that by training the neural net data on the statistical measures of the sensor probe acceleration, information on the particle concentration field can be extracted with a reasonable degree of accuracy.

Distinguishing elastic and inelastic scattering effects in reflection electron energy loss spectroscopy

Reflection electron energy loss spectra (REELS) have been measured for 500 eV electrons backreflected from a polycrystalline Au surface for a few special experimental configurations where the scattering angle was changed without changing the incidence and emission angle. Since effects of inelastic scattering are independent of the scattering angle, but depend on the incidence and emission angle only, this allows one to distinguish the effects of elastic and inelastic scattering in the raw experimental data. For identical incidence and emission angles, the spectra recorded at different scattering angles are found to be significantly different. This finding provides direct experimental proof for the influence of elastic scattering on the shape of electron energy loss spectra. In other words, the energy and emission direction of backscattered electrons are correlated even in the absence of diffraction effects and in spite of the fact that changes in the electron energy and direction of motion in individual collisions are uncorrelated. The impact of this finding for analysis of REELS spectra is discussed.

Inundation flow velocity of tsunami on land

AbstractAn estimation of tsunami inundation flow velocity is one of the most challenging issues among tsunami research. Based on field data of inundation depth and inundation flow velocity u estimated using Bernoulli's theorem and inundation depth, fundamental characteristics of the relationship between inundation flow velocity and inundation depth are examined. Fundamental characteristics of the velocity coefficient where g is gravitational acceleration, hf and hr are inundation depths at the front and the back of structures such as a rectangular building with vertical walls, respectively) implicitly included in the relationship are examined through hydraulic experiments. As a result, Cv = 0.6 is recommended as its simple and practical value. It is confirmed through these examinations that the Froude number, defined by where , ranges 0.7–2.0, and when Cv = 0.6 is adopted this Froude number ranges 0.42–1.2. By using the relationship and Cv = 0.6, two simple and practical relationships are presented for two cases where inundation flow velocity exerts the largest or the smallest fluid force on structures. These relationships can be used to roughly grasp the practical side of tsunami damage, and estimate fluid force acting on individual structures, moving velocity and collision force of floating objects and sediment transport such as boulder and sand. Fundamental characteristics of the waterline (tsunami trace) distribution around/on the typical object model (square pillar, corn and column) are also examined through steady flow experiments, and it is confirmed that the maximum and the minimum values of hf/h0 in the full type model of the square pillar are almost the same as those of hf/hr obtained by field surveys where h0 is uniform flow depth. It is also confirmed that hr ≅ h0 when the Froude number, defined by where u0 is uniform flow velocity, is much less than 1.0. Using a newly defined velocity coefficient, tsunami inundation flow velocity on land can be estimated practically and would be useful for checking proposed sediment transport models that are now being developed by tsunami geologists.

Hydrogen reactivity toward carbon monoxide under mechanochemical processing

The study focuses on the hydrogenation of carbon monoxide over Co–Fe-based catalysts. The catalytic reactions were performed under both isothermal and mechanical activation conditions and their rates estimated by monitoring the gradual consumption of carbon monoxide. Aimed at carrying out a sound comparison, the rate of mechanically activated processes was referred to individual collisions by normalizing its value to the amount of powder involved in individual collisions and to the time interval of ongoing deformation. This allowed to point out that the amount of carbon monoxide converted per unit of catalyst mass and unit of time under mechanical activation conditions is at least four orders of magnitude larger than the one reacted under thermal activation conditions. This result is tentatively connected with the generation of local excited states at the catalyst surface.

Model differential cross section of elastic scattering of electrons by atoms in the Monte Carlo simulation of the passage of electrons in a substance

A new model differential cross section is proposed for describing elastic scattering of electrons in simulating the passage of electrons through a substance by the Monte Carlo method. This differential cross section correctly describes the first and second transport scattering cross sections, but is characterized by the total elastic scattering cross section much smaller than the actual value of the total elastic scattering cross section. The application of this differential cross section makes it possible to considerably reduce the number of elastic collisions in the Monte Carlo simulation of passage of electrons in a substance and to model the passage of high-energy electrons using the individual collision model.

Density of displacement cascades for cluster ions: An algorithm of calculation and the influence on damage formation in ZnO and GaN

A method of statistical calculation of parameters of averaged individual collision cascades formed by cluster ions composed of a small number of atoms is suggested. The results of calculations are compared with experimental data on the accumulation of structural damage in ZnO and GaN irradiated with PFn ions (n = 0, 2, 4) with the specific energy of 1.3 keV/amu at room temperature. It is shown that, for ZnO, the density of the displacement cascade does not affect the concentration of stable postimplantation defects in the region of the bulk peak, but significantly affects this concentration in the near-surface region. For GaN, as the displacement-cascade density increases, both an increase in the concentration of stable defects in the region of the bulk maximum of the defect concentration and an increase in the thickness of the surface’s amorphous layer are observed.

Effects of the density of collision cascades: Separating contributions from dynamic annealing and energy spikes

We present a quantitative model for the efficiency of the molecular effect in damage buildup in semiconductors. Our model takes into account only one mechanism of the dependence of damage buildup efficiency on the density of collision cascades: nonlinear energy spikes. In our three-dimensional analysis, the volume of each individual collision cascade is divided into small cubic cells, and the number of cells that have an average density of displacements above some threshold value is calculated. We assume that such cells experience a catastrophic crystalline-to-amorphous phase transition, while defects in the cells with lower displacement densities have perfect annihilation. For the two limiting cases of heavy (500 keV/atom 209Bi) and light (40 keV/atom 14N) ion bombardment of Si, theory predictions are in good agreement with experimental data for a threshold displacement density of 4.5 at.%. For intermediate density cascades produced by small 2.1 keV/amu PF n clusters, we show that dynamic annealing processes entirely dominate cascade density effects for PF 2 ions, while energy spikes begin contributing in the case of PF 4 cluster bombardment.