Grid Radius Research Articles

Investigating the effect of changing parameters in the IEC device in comparative study

Kinetic simulations have been performed on an Inertial Electrostatic Confinement Fusion (IECF) device. These simulations were performed using the particle-in-cell (PIC) method to analyze the behavior of ions in an IEC device and the effects of some parameters on the Confinement Time (CT). CT is an essential factor that significantly contributes to the IEC's performance as a nuclear fusion device. Using the PIC method, the geometry of a two-grided device with variable grid radius, the number of cathode grid rings, variable pressure and different dielectric thickness for the feed stalk was simulated. In this research, with the development of previous works, the interaction of particles was simulated and compared with previous results. The simulation results are in good agreement with the previous results. In these simulations, it was found that with the increase of the dielectric thickness of the feed stalk, the electric field was weakened and as a result, the confinement time was reduced. On the other hand, with the increase of the cathode radius, the confinement time increased. Using the results, an IEC device can be designed with higher efficiency and more optimal CT for ions.

The influence of number of grid points and radius increments in determining safety factor and estimated sliding volume on three-dimensional slope stability analysis

The existence of geometric complexity in the longitudinal direction makes 3D Limit Equilibrium Method (LEM) able to depict conditions in the field well and obtain Safety Factor (SF) that is more representative than the 2D limit equilibrium method. Safety factor calculations are not only influenced by the Direction of Sliding (DoS), but also by the location of the slip surface. Therefore, determining the location of the slip surface is important in the 3D limit equilibrium method. In this study, the method used for generating slip surfaces is a grid search where variations are made on the number of grid points and the radius increments to determine the effect of these two variables on the determination of safety factor and estimated sliding volume. Based on the results of the study, it can be stated that the greater the number of grid points and the radius increments, the estimated sliding volume will be more precise, while the calculation of safety factor is only affected by the number of grid points where the greater the number of grid points, the search of critical slip surface will be more accurate.

High-current-density gas ion ribbon beam formation

Experimental results are presented to demonstrate the possibility of forming extended repetitively pulsed low-energy gaseous ion beams with a notably high current density. The symbiosis of plasma-immersion extraction of ions and their subsequent ballistic focusing in the semi-cylindrical geometry of the focusing system was first used to form a high-density nitrogen and argon ion ribbon beam. The gas-discharge plasma was formed using a hot-cathode-arc discharge-based modified extended source. A nitrogen and argon ion beam was steadily formed at bias potentials of an amplitude up to 1000 V and a pulse duration of 2–80μs at a pulse frequency of 103-104 pulses/s. In the experiments, an inverse change in current amplitude of the focused ion beam was observed with respect to the initial nitrogen and argon plasma densities. The change in the current ratio formed by the nitrogen and argon ion beams in comparison with the initial plasma density is associated with the effect of the ion atomic mass on a high-voltage sheath formation near the grid electrode and the ratio of the sheath width and grid cell dimensions. An argon ion beam with a current of 0.35 A and a nitrogen ion beam with a current of 0.6 A at a focused ribbon beam length of 23 cm were obtained by installing a grid focusing system in the form of a partial cylindrical surface (radius 7.5 cm) at 35 cm from the gas-discharge plasma generator output. A decrease in distance to 20 cm ensured an increase in argon ion current to 0.8 A and nitrogen ion current to 1.3 A. The maximum ion current density at a distance that corresponded to the cylindrical grid radius for nitrogen and argon ions exceeded 0.08 A/cm2 and 0.05 A/cm2, respectively.

Circumbinary discs: Numerical and physical behaviour

We study the evolution of circumbinary disks under the gravitational influence of the binary using two-dimensional hydrodynamical simulations to investigate the impact of disk and binary parameters on the dynamical aspects of the disk. To distinguish between physical and numerical effects we apply three hydrodynamical codes. First we analyse in detail numerical issues concerning the conditions at the boundaries and grid resolution. We then perform a series of simulations with different binary (eccentricity, mass ratio) and disk parameters (viscosity, aspect ratio) starting from a reference model with Kepler-16 parameters. Concerning the numerical aspects we find that the inner grid radius must be of the order of the binary semi-major axis, with free outflow conditions applied such that mass can flow onto the central binary. A closed inner boundary leads to unstable evolutions. We find that the inner disk turns eccentric and precesses for all investigated physical parameters. The precession rate is slow with periods ($T_\mathrm{prec}$) starting at around 500 binary orbits ($T_\mathrm{bin}$) for high viscosity and large $H/R$ where the inner hole is smaller and more circular. Reducing $\alpha$ and $H/R$ increases the gap size and $T_\mathrm{prec}$ reaches 2500 $T_\mathrm{bin}$. For varying binary mass ratios $q_\mathrm{bin}$ the gap size remains constant whereas $T_\mathrm{prec}$ decreases for increasing $q_\mathrm{bin}$. For varying binary eccentricities $e_\mathrm{bin}$ we find two separate branches in the gap size and eccentricity diagram. The bifurcation occurs at around $e_\mathrm{crit} \approx 0.18$ where the gap is smallest with the shortest $T_\mathrm{prec}$. For $e_\mathrm{bin}$ smaller and larger than $e_\mathrm{crit}$ the gap size and $T_\mathrm{prec}$ increase. Circular binaries create the most eccentric disks.

Integer realizations of disk and segment graphs

A disk graph is the intersection graph of disks in the plane, a unit disk graph is the intersection graph of same radius disks in the plane, and a segment graph is an intersection graph of line segments in the plane. Every disk graph can be realized by disks with centers on the integer grid and with integer radii; and similarly every unit disk graph can be realized by disks with centers on the integer grid and equal (integer) radius; and every segment graph can be realized by segments whose endpoints lie on the integer grid. Here we show that there exist disk graphs on n vertices such that in every realization by integer disks at least one coordinate or radius is 22Ω(n) and on the other hand every disk graph can be realized by disks with integer coordinates and radii that are at most 22O(n); and we show the analogous results for unit disk graphs and segment graphs. For (unit) disk graphs this answers a question of Spinrad, and for segment graphs this improves over a previous result by Kratochvíl and Matoušek.

Optimization of Fast-Decodable Full-Rate STBC with Non-Vanishing Determinants

Full-rate STBC (space-time block codes) with non-vanishing determinants achieve the optimal diversity-multiplexing tradeoff but incur high decoding complexity. To permit fast decoding, Sezginer, Sari and Biglieri proposed an STBC structure with special QR decomposition characteristics. In this paper, we adopt a simplified form of this fast-decodable code structure and present a new way to optimize the code analytically. We show that the signal constellation topology (such as QAM, APSK, or PSK) has a critical impact on the existence of non-vanishing determinants of the full-rate STBC. In particular, we show for the first time that, in order for APSK-STBC to achieve non-vanishing determinant, an APSK constellation topology with constellation points lying on square grid and ring radius √m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> +n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (m,n integers) needs to be used. For signal constellations with vanishing determinants, we present a methodology to analytically optimize the full-rate STBC at specific constellation dimension.

A stationary multi-component cathode modeling and ion trajectories for an inertial electrostatic confinement fusion device

A new cathode modeling with stationary multi-component cathode approach is suggested for an inertial electrostatic confinement fusion device and some preliminary simulation studies based on the potential function of this cathode have been presented. The ions are accelerated due to the Coulomb force on a 2D plane and the central grid is assumed to have 6 point-wise and negatively charged at the middle. The model includes a repulsive force that stems from the screening effect of atoms at the vicinity of cathode. The simulations have proven that the particle trajectories are highly complex in the new potential well; in fact, the prediction of the particle route is observed to be strictly dependent on the control parameters such as the grid radius, ion current, voltage and initial position of the ion. Copyright © 2010 John Wiley & Sons, Ltd.

New radius compensation algorithm based on Delaunay triangulation

Reasonable radius compensation can improve the precision of reverse engineering greatly. Based on the analysis of existing radius compensation algorithms and corresponding advantages and disadvantages,a new algorithm of triangle grid radius compensation was proposed by introducing the idea of Delaunay triangulation. At the same time,some key techniques such as criteria for triangulation optimization and treatment of boundary points were expounded in detail. At last,radius compensation of data points on blade surface of supercharger impeller was achieved.

Spatial variations in prostate tissue histology as measured by a tactile resonance sensor

In recent years, tactile sensors based on piezoelectric resonance sensor technology have been used for medical diagnosis where the sensor's stiffness-measuring properties can reflect tissue pathology. The change in the frequency of the resonating system and the change in force when contact is made with tissue are used as a stiffness parameter. Earlier stiffness measurements of prostate tissue in vitro demonstrate variations related to tissue composition. In this study, measured stiffness from two human prostate specimens was compared to histological composition of prostate tissue below and around the measurement points. Tissue stiffness was measured with the resonance sensor system. Tissue composition was measured at four different depths in the tissue specimen using a microscopic-image-based morphometrical method. With this method, the proportion of tissue types was determined at the points of intersections in a circular grid on the images representing each measurement point. Numerical values were used for weighting the tissue proportions at different depths in the tissue specimen. For an impression depth of 1.0 mm, the sensing depth in this study was estimated to be 3.5–5.5 mm. Stiffness variations due to horizontal tissue variations were investigated by studying the dependence of the size of the circular grid area relative to the contact area of the sensor tip. The sensing area (grid radius) was estimated to be larger than the contact area (contact radius) between the sensor tip and the tissue. Thus, the sensor tip registers spatial variations in prostate tissue histology, both directly below and lateral to the tip itself. These findings indicate that tumours around the sensor tip could be detected, which in turn supports the idea of a future resonance-sensor-based clinical device for detecting tumours and for guiding biopsies.

Influence of grid and target radius and ion–neutral collisions on grid-enhanced plasma source ion-implantation process

Grid-enhanced plasma source ion implantation (GEPSII) is a newly proposed technique for inner surface modification of materials with cylindrical geometry. In this paper, a collisional fluid model is used to investigate the ion sheath dynamics between the grid electrode and the inner surface of a cylindrical bore during the GEPSII process. Assuming the initial ion density along the radial direction is not uniform but determined by diffusion mechanisms, the effects of grid electrode radius, target radius and ion–neutral collisions on the ion dose and impact energy are investigated by solving fluid equations for ions coupled with Boltzmann assumption for electrons and Poisson's equation. The results show that small gap distance between grid electrode and target is favourable to increase the ion dose and impact energy on the target. In addition, ion–neutral collisions can reduce both the ion dose and impact energy.

Optimization of IEC Grid Design for Maximum Neutron Production

Two different, complementary approaches were taken to determine the effects of an Inertial Electrostatic Confinement (IEC) grid`s design on the neutron production rate of the device. A semi-empirical formula developed from experimental data predicts the neutron yield of an IEC device, given the chamber size, grid radius and transparency, and operating voltage and current. Results from the IXL computer program support some of the scalings found in the semi-empirical formula. A second formula was also developed that predicts the neutron yield of an IEC device using grid design parameters and the ion core radius. The SIMION computer program was used to calculate the ion core radius. These formulas are useful tools for designing grids that will maximize the neutron yield for IEC devices. 7 refs., 9 figs.

Finite grid radius and thickness effects on retarding potential analyzer measured suprathermal electron density and temperature

The effect of finite grid radius and thickness on the electron current measured by planar retarding potential analyzers (RPAs) is analyzed numerically. Depending on the plasma environment, the current is significantly reduced below that which is calculated using a theoretical equation derived for an idealized RPA having grids with infinite radius and vanishingly small thickness. A correction factor to the idealized theoretical equation is derived for the Pioneer Venus (PV) orbiter RPA (ORPA) for electron gasses consisting of one or more components obeying Maxwell statistics. The error in density and temperature of Maxwellian electron distributions previously derived from ORPA data using the theoretical expression for the idealized ORPA is evaluated by comparing the densities and temperatures derived from a sample of PV ORPA data using the theoretical expression with and without the correction factor.

A determination of the fundamental types of electron oscillations in a triode valve

It is confirmed experimentally that with a retarding-field triode, electron oscillations can be maintained whose wave-lengths are determined completely by the external circuit (Gill-Morell oscillations); and that, in addition, oscillations can be obtained with wave-lengths completely independent of the external circuit, provided the latter does not approach resonance with them (Barkhausen-Kurz oscillations). The dependence of the Barkhausen-Kurz oscillations on the valve-dimensions and operating conditions is examined in detail. It is found that for any given set of conditions there are not one, but two possible fundamental wave-lengths: type A, of shorter wave-length, and type B, of longer wave-length, both of which may give harmonics. For any valve of grid radius rg, and at constant anode voltage, characteristic curves λA Vg1/2/rg = FA(ig/i0) and λB Vg1/2/rg = FB(ig/i0) may be obtained, where λA and λB are the wave-lengths of the A- and B-type oscillations, Vg is the grid voltage, and ig/i0 is the degree of saturation of the grid-cathode space. Except for certain limiting conditions, the dependence of FA and FB on valve-dimensions and operating conditions is small, a slight decrease being obtained with decrease of the ratio (grid spacing)/(grid radius), or with decrease of grid voltage. By application of the theory developed in an earlier paper, the shape of the characteristic A curve establishes that the A-type oscillations are due to the periodic transit of electrons between the cathode and virtual cathode. The shape of the characteristic B curve, on the other hand, shows that the B-type oscillations are not due to any such transit of electrons, and leads to the conclusion that they are determined by the resonant circuit formed by the grid-plate capacity in parallel with the equivalent inductance of the electron cloud between these electrodes.