Minimum Distance Of Approach Research Articles

Movement of liquid droplets in a shear flow

The problem of the motion of a particle around a particle in a shear flow for the conditions of weightlessness and normal earth gravity is considered. The cases where the particle density is greater or less than the density of the main buffer moving fluid (oil particles in water and water particles in oil) are presented. On the basis of numerical modeling, the nature of the influences of gravitational, viscous, lifting and frontal forces on the trajectory of fluid particles in a shear fluid flow are shown. of diameter particles. For the considered liquid particles and stratification of the shear velocity field It is established that the minimum distance of approach of liquid droplets is equal approximately 0.07 of diameter particles.

Methods and algorithms for classifying air targets by importance based on data from an airborne radar system Part 1. Two-stage ranking of air targets according to the degree of danger during the operation of radar in the multipurpose tracking mode

Classification of air targets by rank of importance is the basis for ensuring situational awareness of pilots (crew members) of military aircraft, therefore, the problem of increasing the reliability of target classification is very urgent. The requirement to provide the pilot (crew) with full situational awareness means providing him with complete and reliable information about tactical, electronic, navigation situations and the technical condition of on-board systems. It should be noted that when classifying air targets according to the rank of importance, dangerous, favorable for attack and non-dangerous targets are currently usually distinguished. Specific tasks of classifying air targets by importance rank belong to the class of object recognition tasks. In modern aviation radio-electronic complexes, the classification of air targets according to the rank of importance is usually carried out according to the data of on-board radar systems, as well as electronic intelligence systems and optoelectronic systems. It should be noted that one of the main information modes of functioning of modern and future radar systems is the multipurpose tracking mode, in which an airborne radar can simultaneously track a large number of targets in its area of responsibility. In the conduct of hostilities, ensuring one's own security is a priority task for aircraft of various purposes. In this case, the role of dangerous air targets can be not only targets belonging to the opposing side, but also their own aircraft in dangerous encounters, in which a collision can occur between them. Therefore, the problem of preventing dangerous encounters and preventing aircraft collisions with each other becomes one of the key problems in group operations of military aviation. It should be noted that by now there are various methods of assessing goals according to the degree of their danger, but there is no systematic presentation of them. An attempt is made in the article to give a systematized presentation of new methods for solving this problem, based on a two-stage decision-making on the predicted minimum distance of closest approach and the time to reach it. Based on this approach, the following are considered: the method of subjective reduction of private indicators; procedures for determining the hazard indicators of air targets in the antenna coordinate system; rules for making decisions on the degree of danger of targets, taking into account their possible maneuver; – the composition of information support for solving this problem has been determined.

Local spin dynamics of iron oxide magnetic nanoparticles dispersed in different solvents with variable size and shape: A 1H NMR study.

Colloidal magnetic nanoparticles (MNPs) based on a nearly monodisperse iron oxide core and capped by oleic acid have been used as model systems for investigating the superparamagnetic spin dynamics by means of magnetometry measurements and nuclear magnetic resonance (1H NMR) relaxometry. The key magnetic properties (saturation magnetization, coercive field, and frequency dependent "blocking" temperature) of MNPs with different core size (3.5 nm, 8.5 nm, and 17.5 nm), shape (spherical and cubic), and dispersant (hexane and water-based formulation) have been determined. 1H NMR dispersion profiles obtained by measuring the r1 (longitudinal) and r2 (transverse) nuclear relaxivities in the frequency range 0.01-60 MHz confirmed that in all samples the physical mechanisms that drive the nuclear relaxation are the Néel reversal at low temperature and the Curie relaxation at high frequency. The magnetization reversal time at room temperature extracted from the fitting of NMR data falls in the typical range of superparamagnetic systems (10-9-10-10 s). Furthermore, from the distance of minimum approach we could conclude that water molecules do not arrive in close vicinity of the magnetic core. Our findings contribute to elucidate the local spin dynamics mechanisms in colloidal superparamagnetic nanoparticles which are useful in biomedical application as, e.g., contrast agents for magnetic resonance imaging.

Gliese 710 will pass the Sun even closer

Context. First results based on Gaia data show that the well-known star Gliese 710 will be the closest flyby star in the next several Myrs and its minimum distance from the Sun will be almost five times smaller than that suggested by pre-Gaia solution.Aims. The aim of this work is to investigate the proximity parameters and the influence of the close approach of Gliese 710 on the basis of Gaia DR1. Furthermore, we compare new results with previous works based on HIP2 and Tycho 2 catalogues to demonstrate how Gaia improves the accuracy of determination of such phenomena.Methods. Using a numerical integration in an axisymmetric Galactic model, we determine new parameters of the close encounter for Gliese 710. Adding ten thousand clones drawn with the use of a covariance matrix, we estimate the most probable position and velocity of this star at the minimum distance from the Sun.Results. Our calculations show that Gliese 710 will pass 13365 AU from the Sun in 1.35 Myr from now. At this proximity it will have the brightness of −2.7 mag and a total proper motion of 52.28 arcsec per year. After the passage of Gliese 710 we will observe a large flux of new long-period comets. Thanks to the Gaia mission, the uncertainties of the minimum distance and time of the close approach are several times smaller than suggested by previous works based on data from earlier observations.

A brief peripheral motion contrast threshold test predicts older drivers’ hazardous behaviors in simulated driving

Our research group has previously demonstrated that the peripheral motion contrast threshold (PMCT) test predicts older drivers’ self-report accident risk, as well as simulated driving performance. However, the PMCT is too lengthy to be a part of a battery of tests to assess fitness to drive. Therefore, we have developed a new version of this test, which takes under two minutes to administer. We assessed the motion contrast thresholds of 24 younger drivers (19–32) and 25 older drivers (65–83) with both the PMCT-10min and the PMCT-2min test and investigated if thresholds were associated with measures of simulated driving performance. Younger participants had significantly lower motion contrast thresholds than older participants and there were no significant correlations between younger participants’ thresholds and any measures of driving performance. The PMCT-10min and the PMCT-2min thresholds of older drivers’ predicted simulated crash risk, as well as the minimum distance of approach to all hazards. This suggests that our tests of motion processing can help predict the risk of collision or near collision in older drivers. Thresholds were also correlated with the total lane deviation time, suggesting a deficiency in processing of peripheral flow and delayed detection of adjacent cars. The PMCT-2min is an improved version of a previously validated test, and it has the potential to help assess older drivers’ fitness to drive.

Modeling relativistic soliton interactions in overdense plasmas: a perturbed nonlinear Schrödinger equation framework.

We investigate the dynamics of localized solutions of the relativistic cold-fluid plasma model in the small but finite amplitude limit, for slightly overcritical plasma density. Adopting a multiple scale analysis, we derive a perturbed nonlinear Schrödinger equation that describes the evolution of the envelope of circularly polarized electromagnetic field. Retaining terms up to fifth order in the small perturbation parameter, we derive a self-consistent framework for the description of the plasma response in the presence of localized electromagnetic field. The formalism is applied to standing electromagnetic soliton interactions and the results are validated by simulations of the full cold-fluid model. To lowest order, a cubic nonlinear Schrödinger equation with a focusing nonlinearity is recovered. Classical quasiparticle theory is used to obtain analytical estimates for the collision time and minimum distance of approach between solitons. For larger soliton amplitudes the inclusion of the fifth-order terms is essential for a qualitatively correct description of soliton interactions. The defocusing quintic nonlinearity leads to inelastic soliton collisions, while bound states of solitons do not persist under perturbations in the initial phase or amplitude.

Simulation of two counter-propagating helium discharges at atmospheric pressure

This paper presents 2D simulations showing the dynamics of interaction between two counter-propagating helium discharges at atmospheric pressure. The discharges were generated in two glass tubes separated by a few centimeters in ambient air. First, we applied the same voltage to each electrode wrapped around each discharge tube. Simulation results show that discharges ignite in tubes and then propagate, approaching each other without merging, as observed in experiments. Using the optical emission of discharges, we have determined the minimum distance of approach of counter-propagating discharges. This minimum distance is of the order of the tube diameter, and varies with the tube radius and inversely to the applied voltage. For conditions with different applied voltages on the electrodes, simulation results show a connection of both counter-propagating discharges with an increase in the discharge emission in the interaction region. For conditions with a time delay between the voltage applied on both electrodes, based on the optical emission of discharges, we have observed that counter-propagating discharges approach each other without merging. The minimum distance is of the order of the tube diameter, as in the reference case, without time delay between both applied voltages. However, simulation results show that the electron density in the interaction region between both discharge channels is about one order of magnitude higher than that for the reference case.

Optical vortex solitary wave in a bounded nematic-liquid-crystal cell

Modulation theory, based on a Lagrangian formulation of the governing equations, is used to investigate the propagation of a nonlinear, nonlocal optical vortex solitary wave in a finite nematic-liquid-crystal cell. The nematic response to the vortex is calculated using the approach of the method of images (MOI). It is demonstrated that the MOI is a reliable alternative to the usual Fourier series solution as it requires an order of magnitude fewer terms to obtain excellent agreement with numerical solutions. It is found that the cell walls, in addition to repelling the optical vortex solitary wave, as for an optical solitary wave, can destabilize it due to the fixed director orientation at the walls. A linearized stability analysis is used to explain and analyze this instability. In particular, the minimum distance of approach of a stable vortex to the wall is determined from the stability analysis. Good agreement is found with numerical minimum approach distances.

Assembling Neurospheres: Dynamics of Neural Progenitor/Stem Cell Aggregation Probed Using an Optical Trap

Optical trapping (tweezing) has been used in conjunction with fluid flow technology to dissect the mechanics and spatio-temporal dynamics of how neural progenitor/stem cells (NSCs) adhere and aggregate. Hitherto unavailable information has been obtained on the most probable minimum time (∼5 s) and most probable minimum distance of approach (4–6 µm) required for irreversible adhesion of proximate cells to occur. Our experiments also allow us to study and quantify the spatial characteristics of filopodial- and membrane-mediated adhesion, and to probe the functional dynamics of NSCs to quantify a lower limit of the adhesive force by which NSCs aggregate (∼18 pN). Our findings, which we also validate by computational modeling, have important implications for the neurosphere assay: once aggregated, neurospheres cannot disassemble merely by being subjected to shaking or by thermal effects. Our findings provide quantitative affirmation to the notion that the neurosphere assay may not be a valid measure of clonality and “stemness”. Post-adhesion dynamics were also studied and oscillatory motion in filopodia-mediated adhesion was observed. Furthermore, we have also explored the effect of the removal of calcium ions: both filopodia-mediated as well as membrane-membrane adhesion were inhibited. On the other hand, F-actin disrupted the dynamics of such adhesion events such that filopodia-mediated adhesion was inhibited but not membrane-membrane adhesion.

New trends in modern statistical physics

Intermolecular forces are modeled by means of a modified Lennard-Jones potential, introducing a distance of minimum approach, and the effect of intermolecular interactions is accounted for with a self consistent field of the Vlasov type. A Vlasov equation is then written and used to investigate the propagation of perturbations in a liquid. A dispersion relation is obtained and an effect of damping, analogous to what is known in plasmas as "Landau damping", is found to take place.

Wave propagation and Landau-type damping in liquids

AbstractIntermolecular forces are modeled by means of a modified Lennard-Jones potential, introducing a distance of minimum approach, and the effect of intermolecular interactions is accounted for with a self consistent field of the Vlasov type. A Vlasov equation is then written and used to investigate the propagation of perturbations in a liquid. A dispersion relation is obtained and an effect of damping, analogous to what is known in plasmas as “Landau damping”, is found to take place.

Coarse – grained molecular dynamics simulation of cross – linking of DGEBA epoxy resin and estimation of the adhesive strength

In this work we attempt to predict the work of separation of crosslinked diglycidyl ether of bisphenol (A) (DGEBA) adhesive confined between two rigid adherends. To this end we start from merely the molecular structure of DGEBA and coarse grain the molecule into a chain comprised of three superatoms. These three superatom structures are then allowed to crosslink (based on the attainment of a minimum distance of approach) with a coarse grained crosslinker molecule in a Molecular Dynamics (MD) simulation. The crosslinked samples, confined between rigid walls and subjected to slab boundary conditions are pulled apart at a high rate of strain to complete separation. The energy expended in causing complete separation is compared with Linear Elastic Fracture Mechanics estimates and experimental determinations of the work of separation. Our predictions of the value of the work of separation, obtained from only a description of the molecular architecture of DGEBA and the crosslinker molecule, falls within the range of scatter in the experimental measurements. Keywords: Molecular Dynamics, Coarse – Graining, Cross – linking, Adhesion Energy

Equilibrium Electric Double Layer of Charged Spherical Colloidal Particles: Effect of Different Distances of Minimum Ion Approach to The Particle Surface

A study of the equilibrium double layer surrounding charged spherical particles is presented, considering that ions in the suspending medium have a finite size. It is assumed that each ionic species has a different minimum approach distance to the particle surface, while the distance of minimum approach between ions in the bulk has the same value for all ion species. Numerical calculations made using the network simulation method and including all the features of the considered model are presented, together with rigorous analytical results valid for a flat interface and point ions in the bulk electrolyte solution. It is shown that the double-layer parameters are very sensitive to the difference between the minimum approach distances of co-ions and counterions. For negative particles and greater approach distances for co-ions than for counterions, the potential always increases with this difference and, under appropriate circumstances, attains positive values leading to charge reversal. This phenomenon is favored by a high electrolyte concentration, high counterion valences, and low surface charge (in modulus). An analytical expression relating these parameters to the threshold value of the difference between the minimum approach distances of co-ions and counterions to the particle surface is presented.

On the relationship between charge distribution, surface hydration, and the structure of the interface of metal hydroxides

The double layer structure of metal (hydr)oxides is discussed. Charge separation may exist between the minimum distance of approach of electrolyte ions and the DDL domain. The corresponding capacitance value of the outer Stern layer is similar to the capacitance value of the inner Stern layer. The extended Stern model implicitly supports a hydration structure at the near-surface with some discrete layering of water and electrolyte ions. The significance of dipole orientation is analyzed theoretically. Dipole theory in combination with a calculated ion charge distribution is compared with the experimental overall charge distribution. Ion charge distribution for various oxyanions has been calculated applying the Brown bond valence concept to the geometry of surface complexes that have been optimized with MO/DFT calculations. The comparison is done in detail for silicic acid adsorption on goethite. In addition, results are discussed for arsenite, carbonate, sulfate, and phosphate, using the same approach. The dipole correction depends on the charge introduced in a neutral surface by ion adsorption, which differs for the various ions studied. The fractional correction factor ϕ derived for the experimental data agrees with the theoretical value ϕ m = 0.17 ± 0.02 . On an absolute scale, the dipole corrections are usually limited to the range about 0–0.15 v.u. The CD values calculated with MO/DFT are not particularly sensitive (∼0.03 v.u.) to the precise Fe-octahedral geometry, which suggests that a calculated CD is a reasonable approximation in ion adsorption modeling for ill-defined Fe-oxides like HFO and natural Fe oxide materials of soils.

A kinetic approach to the calculation of surface tension of a spherical drop

In literature, surface tension has been investigated mainly from a Thermodynamics standpoint, more rarely with kinetic methods. In the present work, surface tension of drops is studied in the framework of kinetic theory, starting from the Sutherland approximation to Van Der Waals interaction between molecules. Surface tension is calculated as a function of drop radius: it is found that it approaches swiftly an asymptotic value, for radii of several times the distance of minimum approach D of the Sutherland potential. This theoretical asymptotic value is compared to experimental values of surface tension in plane surfaces of a few liquids, and is found in reasonable agreement.

Self-consistent theory of rupture by progressive diffuse damage.

We analyze a self-consistent theory of crack growth controlled by a cumulative damage variable d(t) dependent on stress history, in the quasistatic regime where the sound wave velocity is taken as infinite. Depending upon the damage exponent m, which controls the rate of damage dd/dt~sigma(m) as a function of local stress sigma, we find two regimes. For 0<m<2, the model predicts a finite-time singularity. This retrieves previous results by Zobnin for m=1 and by Bradley and Wu for 0<m<2. To improve on this self-consistent theory which neglects the dependence of stress on damage, we apply the functional renormalization method of Yukalov and Gluzman and find that divergences are replaced by singularities with exponents in agreement with those found in acoustic emission experiments. For m>/=2, the rupture dynamics is not defined without the introduction of a regularizing scheme. We investigate three regularization schemes involving, respectively, a saturation of damage, a minimum distance of approach to the crack tip, and a fixed stress maximum. In the first and third schemes, the finite-time singularity is replaced by a crack dynamics defined for all times but which is controlled by either the existence of a microscopic scale at which the stress is regularized or by the maximum sustainable stress. In the second scheme, a finite-time singularity is again found. In the first two schemes within this regime m>/=2, the theory has no continuous limit.

Chaotic advection near a three-vortex collapse.

Dynamical and statistical properties of tracer advection are studied in a family of flows produced by three point-vortices of different signs. Tracer dynamics is analyzed by numerical construction of Poincaré sections, and is found to be strongly chaotic: advection pattern in the region around the center of vorticity is dominated by a well developed stochastic sea, which grows as the vortex system's initial conditions are set closer to those leading to the collapse of the vortices; at the same time, the islands of regular motion around vortices, known as vortex cores, shrink. An estimation of the core's radii from the minimum distance of vortex approach to each other is obtained. Tracer transport was found to be anomalous: for all of the three numerically investigated cases, the variance of the tracer distribution grows faster than a linear function of time, corresponding to a superdiffusive regime. The transport exponent varies with time decades, implying the presence of multi-fractal transport features. Yet, its value is never too far from 3/2, indicating some kind of universality. Statistics of Poincaré recurrences is non-Poissonian: distributions have long power-law tails. The anomalous properties of tracer statistics are the result of the complex structure of the advection phase space, in particular, of strong stickiness on the boundaries between the regions of chaotic and regular motion. The role of the different phase space structures involved in this phenomenon is analyzed. Based on this analysis, a kinetic description is constructed, which takes into account different time and space scalings by using a fractional equation.

Critical radius in axial channeling

When studying phenomena related to the channeling of charged particles it is of great importance to consider them as functions of the impact parameter. This point of view plays an important role to the interpretation of experimental results as well as to computer simulations. Thus the distance of minimum approach, for which channeling conditions still hold, either under axial or planar channeling is of importance. In the present work we use the Monte-Carlo method to investigate the correlation of the distance of minimum approach of axially channeled particles with the exit angle of those particles from the crystal. We calculated the distance of minimum approach for several incidence angles at different temperatures and for many crystal thickness. The results we obtained prove that the distance of minimum approach has two main properties. (a) It is independent of the crystal thickness and depends only slightly on the incidence angle (as long as the incidence angle does not exceed the Lindhard angle) and slightly decreases with increasing temperature. (b) It agrees with Lindhard’s theory predictions but at the same time it seems that some particles approach too close to the crystal axis without being dechanneled.

Deposition of hairy latex particles onto a glass surface

Hairy latex particles are observed to deposit on a glass surface under conditions for which the DLVO theory predicts no deposition. From electrophoretic mobility and dynamic light scattering experiments it can be concluded that the surfactant-free polystyrene latex particles used in this study are “hairy”, with the length of the hairs being more than 5nm. It is speculated that the hairs can tunnel through the energy barrier and make contact with the glass since deposition occurs when the length of the hairs is comparable to the minimum distance of approach calculated from DLVO theory. Consistent with this model, it is found that the deposition rates increase with salt concentration, while the detachment rates decrease with salt concentration.

Electrodynamic Focusing of Charged Aerosol Particles

An electrodynamic screen for focusing charged particles carried by an airflow stream has been constructed and tested. The screen has the shape of a cone frustum with half-angle of 8° and is 17 cm long. Entrance and exit diameters are 7.0 and 2.5 cm, respectively. Electrodes forming the screen are three 0.71-mm diameter stainless-steel wires configured as a triple-start helix with 2.0-mm pitch. A three-phase power supply drives each wire with a line-to-ground voltage of 2300 V at 350 Hz with a phase difference of 120° between adjacent wires. Test particles of 5.2-μm aerodynamic diameter with electric charge of 1850–6080 elementary units per particle in an aerosol having a mean flow velocity of 4.3×10−2 m/s parallel to the vertically oriented cone axis are confined and focused with essentially no particle loss. Minimum distance of approach of the test particles to the screen, as found from computer simulation of particle trajectories, solution of the particle equations of motion by linear approximation, and experimental observation, are in good agreement.