Rigid Sphere Model Research Articles

Using a motion capture system for spatial localization of EEG electrodes.

Electroencephalography (EEG) is often used in source analysis studies, in which the locations of cortex regions responsible for a signal are determined. For this to be possible, accurate positions of the electrodes at the scalp surface must be determined, otherwise errors in the source estimation will occur. Today, several methods for acquiring these positions exist but they are often not satisfyingly accurate or take a long time to perform. Therefore, in this paper we describe a method capable of determining the positions accurately and fast. This method uses an infrared light motion capture system (IR-MOCAP) with 8 cameras arranged around a human participant. It acquires 3D coordinates of each electrode and automatically labels them. Each electrode has a small reflector on top of it thus allowing its detection by the cameras. We tested the accuracy of the presented method by acquiring the electrodes positions on a rigid sphere model and comparing these with measurements from computer tomography (CT). The average Euclidean distance between the sphere model CT measurements and the presented method was 1.23 mm with an average standard deviation of 0.51 mm. We also tested the method with a human participant. The measurement was quickly performed and all positions were captured. These results tell that, with this method, it is possible to acquire electrode positions with minimal error and little time effort for the study participants and investigators.

Collective-field-corrected strong field approximation for laser-irradiated metal clusters

The strong field approximation (SFA) formulated in terms of so-called ‘quantum orbits’ led to much insight into intense-laser driven ionization dynamics. In plain SFA, the emitted electron is treated as a free electron in the laser field alone. However, with improving experimental techniques and more advanced numerical simulations, it becomes more and more obvious that the plain SFA misses interesting effects even on a qualitative level. Examples are holographic side lobes, the low-energy structure, radial patterns in photoelectron spectra at low kinetic energies and strongly rotated angular distributions. For this reason, increasing efforts have been recently devoted to Coulomb corrections of the SFA. In the current paper, we follow a similar line but consider ionization of metal clusters. It is known that photoelectrons from clusters can be much more energetic than those emitted from atoms or small molecules, especially if the Mie resonance of the expanding cluster is evoked. We develop a SFA that takes the collective field inside the cluster via the simple rigid-sphere model into account. Our approach is based on field-corrected quantum orbits so that the acceleration process (or any other spectral feature of interest) can be investigated in detail.

Mechanisms of Atomic Motion Through Crystalline GeTe

Germanium telluride (GeTe) is an iconic functional material, both in itself and as the parent compound for a range of ternary phase-change data-storage alloys. Long taken to be a “simple” AB compound, crystalline GeTe is today known to contain a large number of germanium vacancies which directly affect the material’s macroscopic properties. Here, we use atomistic simulations to elucidate local mechanisms behind the motion of Ge atoms (and thus, vacancy diffusion) in crystalline GeTe. Transition pathways are computed using the nudged elastic band (NEB) approach at the gradient-corrected level of density-functional theory (GGA-DFT), both for the idealized rhombohedral (R3m) crystal and a number of defective configurations. Besides obvious structural arguments (i.e., beyond a simple rigid-sphere model), the diffusion barriers show a delicate dependence on the material’s electronic structure. The latter is controlled by vacancy formation, Sb adatoms, and charge injection, all of which is discussed in a unifie...

Molecular dynamics approach to sodium–water reaction compensating macroscopic heat and mass flow dynamics for LMFBR safety

AbstractThe potential (reaction) energy and reaction rate of an accidental sodium−water reaction are investigated for fast breeder nuclear reactor safety. The potential energy is calculated using the molecular orbital method with accurate Gaussian Quadratures in the density functional scheme. The gaseous reaction rate analysis focuses on collision theory rather than transition state theory; the latter of which is more for solvents/solutions. The rate constant was derived using classical molecular dynamics (MDs) in two dimensions (2D) with the rigid sphere model. The MD calculation reveals analytic sequences suppressing error accumulations and time consumptions. The 2D result is converted to the 3D value via a corresponding cross section ratio with a form factor, reproducing the experimental value. The availability of microscopic results to macroscopic flow dynamics is appended; renormalizing the kinematic viscosity coefficient with scale‐independent constants. An effective (pseudo‐) MD for the heat transfer is also appended. © 2012 Wiley Periodicals, Inc.

Laser-cluster interaction with subcycle pulses

The interaction of intense laser light with atomic nanoclusters is studied with a rigid sphere model and three-dimensional particle-in-cell simulations for ultrashort laser pulses of pulse durations $\ensuremath{\tau}$ down to one optical period $T$ and below. In this subcycle regime not all conventional pulse models are applicable and may lead to unphysical absorption of laser energy. For allowed pulse models, we show that for a given laser peak intensity, and cluster, the efficiency of laser absorption increases as $\ensuremath{\tau}$ shortens and reaches a maximum value in the subcycle regime. For deuterium clusters, where inner ionization quickly saturates, the absorbed energy and outer ionization reaches a peak at $\ensuremath{\tau}\ensuremath{\approx}0.8T$. For argon clusters, however, such a peak disappears, and energy absorption continues even for $\ensuremath{\tau}<0.8T$ due to additional inner ionization.

An Investigation to Added Mass Force on the Wing of Insect Inspired from a Rigid Sphere Model

There is a force peak at the beginning of each stroke during the insect flight, this force peak contributes a lot to the total aerodynamic force. To build a man made insect inspired man-made micro aero vehicle, this force need to be considered in the aero force model, and this model should as simple as possible in order to be used in feedback real-time control. Here we presented a simplified model to take the medium added mass effect of the wing into account. Simulated results show a high force peak at the beginning of each stroke and are quite similar to the measured forces on the physical wing model which were carried out by Dickinson et.al.

Analysis of Elastic-Plastic Contact Performance of Rigid Sphere Against a Deformable Flat-Effect of Strain Hardness

Problem statement: The present study considers an elastic-plastic contact analysis of a rigid sphere with a deformable flat (Rigid Sphere-model) using finite element analysis. The effect of tangent modulus on the contact behavior of a no adhesive frictionless elastic-plastic contact was analyzed using commercial finite element software ANSYS. Approach: Different materials, in terms of the ratio of Young's modulus to yield strength, had been considered to study the effect of tangent modulus. The Finite Element (FE) contact analysis was carried out by incorporating the various tangent modulus values of different materials. Results: The result clearly shows that for different tangent modulus the material hold different stress values. When this modulus increases the strain hardness value of material was also increased. Conclusion: With increase in tangent modulus, strain hardening resistance to deformation of a material is increased and the material becomes capable of carrying higher amount of load in a smaller contact area.

Ion mobility spectrometry: a personal retrospective

With a background in mass spectrometric studies of gas-phase ion chemistry the atmospheric pressure technology of ion mobility spectrometry (IMS) presented me with challenges and opportunities. Fundamental studies of the parameters that influence the mobility of ions in a low electric field yielded insights about the effects of temperature, drift gas composition and the conformation of ions on the collision cross section. The inadequacy of current rigid-sphere, polarization limit and hard-core models to predict the mobility of ions particularly at low temperature and in heavy drift gases, led to inclusion of additional terms to the hard-core model to account for these effects. These studies eventually resulted in the two monographs entitled “Ion Mobility Spectrometry” and “Ion Mobility Spectrometry –Second Edition” co-authored with Prof. Gary Eiceman and published by Taylor & Francis, CRC Press in 1994 and 2005, respectively. Novel applications for biological and medical applications were developed on the basis of measurement of biogenic amines by IMS, in particular the rapid, accurate and inexpensive diagnosis of vaginal infections.

The effect of temperature on the large field electromechanical response of relaxor ferroelectric 8/65/35 PLZT

Full hysteresis loops for the relaxor ferroelectric 8/65/35 PLZT were measured as a function of temperature. The strain–electric field hysteresis loops go from butterfly-shaped at 25 °C to a non-hysteretic quadratic electrostrictive behavior at 98 °C, while the polarization–electric field hysteresis loops go from open loops to linear as the temperature is increased. The measured strain is plotted as a function of electric displacement for each temperature, with results showing a quadratic relationship below the Curie peak with a nearly temperature-independent electrostrictive coefficient. The observed material behavior is discussed in terms of a rigid sphere model of the defect structure produced by lanthanum doping and the limitations of modeling this material behavior as a second-order phase transition are discussed.

Calculation of the surface tension of salt melts with divalent ions

The surface tensions of alkaline-earth metal halides and alkali metal sulfates and carbonates are calculated. Molten salts are described in terms of a charged rigid sphere model using the generalized mean spherical approximation. The calculated surface tensions of these salts are compared to the experimental data, and fitting parameters are not used in these calculations.

Angular scattering of sound from solid particles in turbulent suspension

Sound scattering by solid particles suspended in a turbulent jet is investigated. Measurements of the scattered amplitude were made in a bistatic geometry at frequencies between 1.5 and 4.0 MHz, and at scattering angles from 95 degrees to 165 degrees relative to the forward direction. Two types of particle were used: nearly spherical lead-glass beads and aspherical natural sand grains. For each particle type, experiments were carried out using approximately 200 and approximately 500 microm median diameter grain sizes, corresponding to 0.7 < or approximately ka < or approximately 4. The sphericity of the sand grains, defined as the ratio of projected perimeter size to projected area size, was 1.08. The lead-glass bead results are consistent with an elastic sphere model. A rigid movable sphere model provides the best fit to the sand data, and the best-fit diameter is within 4% of the equivalent volume size. However, the scattering pattern for sand is systematically smoother than predicted: that is, the undulations in the angular scattering pattern predicted by spherical scatterer theory are present, but muted. This observed departure from spherical scatterer theory is attributed to disruption of the interference among creeping waves by the irregular surfaces of natural sand grains.

A psychophysical evaluation of near-field head-related transfer functions synthesized using a distance variation function

A method for synthesizing near-field head-related transfer functions (HRTFs) from far-field HRTFs measured using an acoustic point-source of sound is presented. Near-field HRTFs are synthesized by applying an analytic function describing the change in the transfer function when the location of a sound source changes from the far-field to the near-field: the distance variation function (DVF). The DVF is calculated from a rigid sphere model and approximates the change in the frequency-dependent interaural level cues as a function of the change in sound source distance. Using a sound localization experiment, the fidelity of the near-field virtual auditory space (VAS) generated using this technique is compared to that obtained by simply adjusting the intensity of the VAS stimulus to simulate changes in distance. Results show improved distance perception for sounds at simulated distances of up to 60 cm using the DVF compared to simple intensity adjustment, while maintaining directional accuracy. The largest improvement for distance perception were for sound sources located to the side and within 40 cm. When intensity was removed as a cue for sound source distance from near-field sounds generated using the DVF, results showed some discrimination of sound source distances but, in general, distance perception accuracy was poor.

Ascent Velocity of Plasmoids Generated by Surface Discharges

The ascent velocity of long-lived plasmoids generated under atmospheric conditions to simulate ball lightning was estimated in [Fussmann et al., Phys. Unserer Zeit 39, 246 (2008) and Jegorov et al., Tech. Phys. 53, 688 (2008): Refs. 1 and 2 in the text, respectively], using a rigid sphere model with poor agreement with the experiment. The plasmoids were, however, deformed. Much better agreement is obtained using the Davies and Taylor formula, which describes the ascent velocity of large spherical-cap bubbles.

Modification of Hertzian behaviour in heavily loaded contact in the DMT regime

The adhesive contact between spheres for a small Tabor parameter is investigated. It is found that the DMT model cannot describe the adhesive contact for a small Tabor parameter. By assuming a new contact distance, the modified Hertzian contact is proposed. For a small Tabor parameter, the rigid-sphere model can describe the adhesive contact behaviour for a small load and the modified Hertzian model can describe the adhesive contact behaviour for a large load.

Theoretical and experimental study of some basic processes in He-TlI and Ne-TlI plasma - asymmetric charge transfer, penning ionization and diffusion

The diffusion coefficients of thallium and iodine atoms in a binary system with helium and neon are calculated on the basis of 12-6 Lenard-Jones and rigid sphere models. Cross-sections and rate constants for thermal energy charge transfer into some Tl+ and I+ excited states are theoretically and experimentally obtained for a gas discharge in He-TlI and Ne-TlI mixtures. Cross-sections and rate constants for Penning ionization into Tl+ and I+ ground and excited states are calculated for Penning collisions with the He and Ne metastable atoms. Since the characteristic constants studied depend on the gas temperature, the radial gas temperature distribution is also calculated through solving the heat conduction equation.

Embedded System Implementation of Sound Localization in Proximal Region

A sound localization method in the proximal region is proposed, which is based on a low-cost 3D sound localization algorithm with the use of head-related transfer functions (HRTFs). The auditory parallax model is applied to the current algorithm so that more accurate HRTFs can be used for sound localization in the proximal region. In addition, head-shadowing effects based on rigid-sphere model are reproduced in the proximal region by means of a second-order IIR filter. A subjective listening test demonstrates the effectiveness of the proposed method. Embedded system implementation of the proposed method is also described claiming that the proposed method improves sound effects in the proximal region only with 5.1% increase of memory capacity and 8.3% of computational costs.

Accuracy of one-dimensional collision integral in the rigid-sphere approximation

Solution of many problems of gas kinetics, transport phenomena, and spectroscopy can be significantly simplified using the linearized Boltzmann equation within so called one-dimensional approximation, in which the collision kernel is averaged over the transverse velocities. The error introduced by this approximation is usually considered to be small, however, no quantitative analysis of its value has been done so far. We study the accuracy of the one-dimensional approximation in a particular problem of calculating spectral line shapes in gases. The inaccuracy is shown to be small in the wings of line, in the cases of light buffer molecules or low collision frequency. For arbitrary parameters the error is calculated numerically within the rigid-sphere model. These results outline the area of applicability of computationally economic one-dimensional approach.

On the DMT theory

The frequent claim that the Tabor parameter μ governs the transition from the DMT theory to the JKR theory is investigated. The change from the simple surface force law σ ∼ A/h 3 of the DMT theory to the Lennard–Jones law σ ∼ A/h 3–B/h 9 of the MDT theory and the numerical solutions is noted, and the ‘adhesive force’ is evaluated for both laws. Except in the limit of zero Tabor parameter, when the Derjaguin theories reduce to the rigid-sphere model, the predictions are consistently worse than assuming the sphere to be rigid. A ‘semi-rigid’ sphere model is proposed, which correctly describes the asymptotic behaviour as μ → 0, but leaves a considerable gap before the JKR theory can be applied.

Collisionless energy absorption in the short-pulse intense laser-cluster interaction

In a previous Letter [Phys. Rev. Lett. 96, 123401 (2006)] we have shown by means of three-dimensional particle-in-cell simulations and a simple rigid-sphere model that nonlinear resonance absorption is the dominant collisionless absorption mechanism in the intense, short-pulse laser cluster interaction. In this paper we present a more detailed account of the matter. In particular we show that the absorption efficiency is almost independent of the laser polarization. In the rigid-sphere model, the absorbed energy increases by many orders of magnitude at a certain threshold laser intensity. The particle-in-cell results display maximum fractional absorption around the same intensity. We calculate the threshold intensity and show that it is underestimated by the common over-barrier ionization estimate.

A study of pinna effect on head‐related transfer functions

For the sound localization, an interaural difference is important. To obtain the desired localization, it is necessary to use a head‐related transfer function (refer to HRTF), which is defined as the transfer function between a sound source and a surface of the ear drum. In our previous work, as far as in the case of reproducing the virtual sound source in the horizontal plane, it is confirmed to be capable of remarkable localization by using the numeric data calculated by a rigid sphere head model instead of a dummy head microphone. However, it is necessary to solve the problem of the front back confusion and the sound localization of the vertical plane. For that, it might be essential to add the pinna information to the rigid sphere model, to examine how each part of the pinna is related to the localization.