Two-dimensional Target Research Articles

FIBSIM – dynamic Monte Carlo simulation of compositional and topography changes caused by focused ion beam milling

A new simulation program is presented for focused ion beam (FIB) induced sputtering in two-dimensional targets. The model combines dynamic Monte Carlo simulation of the collision cascades with cell-based topography simulation. This approach takes the nonlocal nature of the sputtering process into account, and treats doping, damage formation and compositional changes self-consistently with the evolution of the surface. Two applications are presented: erosion of a sample edge, and milling of a hole into a multilayer target.

A Monte Carlo study of the rough-sea-surface influence on the radar scattering from two-dimensional ships

The generalized forward-backward (GFB) method was introduced in Pino et al. (1999) for computing the electromagnetic scattering from two-dimensional targets on a rough surface. The GFB method is used in this article to generate numerical data for a Monte Carlo simulation of the horizontally polarized radar cross section (RCS) of two-dimensional ship-like targets on random rough sea surfaces. The RCS is computed as a function of the incidence angle and wind speed for a large number of surface realizations. It is found that the mean RCS of a given target on a rough surface is generally lower than or equal to the RCS of the same target on a flat surface, while the maximum RCS is usually greater than or equal to the flat-surface case. It is also observed that the variations in the RCS introduced by the rough surface become less significant as the elevation angle approaches grazing.

Correction to: "Novel diffraction tomographic algorithm for imaging two-dimensional targets buried under a lossy earth"

The paper by T. J. Cui and W. C. Chew, IEEE Trans. Geosci. Remote Sensing, vol. 38, p.2033-41 (2000) is corrected. The authors, in that paper, defined the branch cut of K/sub ay/ and k/sub by/ in an equation (7) as Re(k/sub ay/,/sub by/)/spl ges/0 and Im(k/sub ay/,/sub by/)/spl ges/0 to make the Sommerfeld-like integral in another equation(5) satisfy the radiation condition. In the inverse-Fourier expression of yet another equation (24), however, they had to choose the branch cut of k/sub by/ in a different way, where Re(k/sub by/)/spl ges/O and Im(k/sub ay/,/sub by/)/spl les/, so that the integral in this equation can be convergent. Hence, the k/sub by/ in equation (27) must be set in different branch cuts. Although such a procedure gave correct reconstruction results, the mathematical interpretation was confusing. In this correspondence, the authors now modify the mathematical interpretation so that it is clear and easily understood.

Novel diffraction tomographic algorithm for imaging two-dimensional targets buried under a lossy Earth

A novel diffraction tomographic algorithm has been proposed to detect two-dimensional (2D) dielectric cylinders buried under a lossy Earth. In this algorithm, the air-Earth interface has been taken into account and the exact treatment of Sommerfeld-like integrals has been considered. Using the algorithm, all locations, shapes, and dielectric properties of buried cylinders can be accurately reconstructed under the low-contrast condition. For high-contrast targets, this algorithm can also be used to determine their locations and approximate their dielectric properties. Due to the use of fast Fourier transforms to implement the problem, this algorithm is very fast and quite tolerant to the error of measurement data. Numerical examples are given to show the validity of the algorithm.

Grassmannians, calibrations and 5-brane intersections

We present a geometric construction of a newclass of hyper-Kähler manifolds with torsion. This involvesthe superposition of the four-dimensional hyper-Kählergeometry with torsion associated with the NS-5-brane along quaternionic planes inℍk. We find the moduli space of these geometries and showthat it can be constructed using the bundle space of thecanonical quaternionic line bundle over a quaternionic projective space.We also investigate several special cases which are associatedwith certain classes of quaternionic planes in ℍk. We then show that the eight-dimensional geometries we have found can be constructed using quaternioniccalibrations. We generalize our construction to superpose the same four-dimensionalhyper-Kähler geometry with torsion along complex planes inℂ2k.We find that the resulting geometry is Kähler with torsion.The moduli space of these geometries is also investigated.In addition, the applications of these new geometries to M-theoryand sigma models are presented.In particular, we find new solutions of IIA supergravity with the interpretation ofintersecting NS-5-branes at {Sp}(2)-angles on a string and show that they preserve 3/32, 1/8, 5/32and 3/16of supersymmetry. We also show that two-dimensional sigma modelswith target spaces above the manifolds have (p,q) extendedsupersymmetry.

High resolution parametric modelling for two-dimensional radar target using prony algorithm

On the conditions of low-resolution radar, a parametric model for two-dimensional radar target is described here according to the theory of electromagnetic scattering and the geometrical theory of diffraction. A high resolution estimation algorithm to extract the model parameters is also developed by building the relation of the scattering model and Prony model. The analysis of Cramer-Rao bound and simulation show that the method here has better statistical performance. The simulated analysis also indicates that the accurate extraction of the diffraction coefficient of scattering center is restricted by signal to noise ratio, radar center frequency and radar bandwidth.

Duality-invariant class of two-dimensional field theories

We construct a new class of two-dimensional field theories with target spaces that are finite multiparameter deformations of the usual coset G/ H-spaces. They arise naturally, when certain models, related by Poisson–Lie T-duality, develop a local gauge invariance at specific points of their classical moduli space. We show that canonical equivalences in this context can be formulated in loop space in terms of parafermionic-type algebras with a central extension. We find that the corresponding generating functionals are non-polynomial in the derivatives of the fields with respect to the space-like variable. After constructing models with three- and two-dimensional targets, we study renormalization group flows in this context. In the ultraviolet, in some cases, the target space of the theory reduces to a coset space or there is a fixed point where the theory becomes free.

Observability of target tracking with range-only measurements

A necessary and sufficient condition for local system observability, a prerequisite to target motion analysis, is presented in this technical communication for two-dimensional manoeuvring target tracking with range-only measurements from a single observer. The approach taken in this paper utilizes the Fisher information matrix developed from the analytical treatment of system dynamics and noisy measurement equations established in a modified polar coordinate system. The analytical results of this paper are demonstrated by a series of simulation studies for applications on naval surface vehicle engagements.

Spatiotemporal properties of saccades elicited by two-dimensional target position

Spatiotemporal properties of saccades elicited by two-dimensional target position

A finite element electrical impedance imaging system for binary media: 3. differential discrimination and separate effects for 2-d and 3-d objects

This paper, the third and final in this series, describes both two- and three- dimensional experimental methods and results. In addition it is shown that differing sensitivity produces differing contrast of similar targets and similar contrast of differing targets, depending on the location in the field being imaged. Furthermore, it has been found that the contrast contour which best describes the area of a target is correlated on the basis of contrast ratio – the ratio of the maximum target resistivity computed relative to that of the homogeneous background. Both quasi-three-dimensional and two-dimensional targets in both 2-D and 3-D phantoms produce virtually identical results. Truly 3-D targets, however, produce quite different results, presumably due to current flow in the third dimension around the target. Increasing the mesh-size and number of iterations, and utilizing boundary optimization are all shown to improve the resultant images. Finally, we show the ability of the system to image a “moving” three-dimensional shape.

Simulation of plasma-based ion implantation of a sawtooth target

Plasma-based ion implantation of a two-dimensional target consisting of a periodic array of symmetric, 90°, triangular sawteeth is studied using a particle-in-cell plasma simulation. The average ion flux, ion impact angle, ion impact energy and the energy-resolved dose are computed. When the sheath width is large compared to the tooth size, the sheath edge becomes planar, the ion flux is nearly uniform and ions impact the surface of the target at 45°. The incident dose is greatest near the convex corner, and least in the concave corner.

A Novel Method for Microwave Imaging of Dielectric Cylinder in Layered Media

A novel method for microwave imaging of lossless two-dimensional dielectric targets buried in layered media using time-domain scattering data with or without the effect of random noise is presented in this paper. It is an iterative method derived using volume equivalence principle, variation principle, Fourier transform. We name it as time-domain variational iterative method (TVIM). In each iteration, both the direct and inverse problems are solved once. The direct problem is solved by finite-difference time domain (FDTD) method and the inverse problem is solved iteratively. Numerical results show that TVIM performs much better than our former method. Those factors which make TVIM perform better are also investigated.

A near-resonance decoupling approach (NRDA) for scattering solution of near-resonant structures

The generalized network formulation is applied in combination with the method of moments to calculate the electromagnetic scattering from conducting objects containing near-resonant open-ended cavities. The presence of the cavity increases the iteration number in conjugate gradient iterations due to the near-resonant modes and the multiple wave bounces inside the cavity. The equivalence principle is used to separate the cavity region from the rest of the object, allowing an independent solution of the cavity problem by a direct inversion algorithm using a connection scheme. The solution of the cavity is then represented by a generalized admittance matrix. Numerical results for two-dimensional (2-D) composite targets show that the iteration number can be reduced significantly for objects containing long cavities. This algorithm can also be applied to three-dimensional problems.

Bethe stopping power theory for fast ions moving through two-dimensional targets: harmonic oscillator model

On the basis of the first-order Born approximation, we obtain Bethe's expression of the electronic stopping power for fast ions moving through two-dimensional targets. For a two-dimensional harmonic oscillator as a target, the numerical results show that in the high-velocity limits the stopping power is proportional to the projectile velocity, which agrees with that predicted by the linear-response dielectric theory.

A numerical study of the RG equation for the deformed O(3) nonlinear sigma model

The Renormalization Group equation describing the evolution of the metric of the nonlinear sigma model poses some nice mathematical problems involving functional analysis, differential geometry and numerical analysis. In this article we briefly report some results obtained from the numerical study of the solutions in the case of a two-dimensional target space (deformation of the O(3) σ-model In particular, our analysis shows that the so-called sausages define an attracting manifold in the U(1)-symmetric case, at one-loop level. Moreover, data from two-loop evolution are used to test the association (Fateev, Onofri and ALB. Zamolodchikov, Nucl. Phys. B 406 (1993) 521) between the so-called SSM η field theory and a certain U(1)-symmetric, factorized scattering theory (FST).

Model of two-dimensional quantum gravity in the strong coupling regime.

A model of two-dimensional quantum gravity that is the analog of the tensionless string is proposed. The gravitational constant ($k$) is the analog of the Regge slope ($\alpha^{'}$) and it shows that when $k \rightarrow \infty$, $2D$ quantum gravity can be understood as a tensionless string theory embeded in a two-dimensional target space. The temporal coordinate of the target space play the role of time and the wave function can be interpreted as in standard quantum mechanics.

Hyalomma truncatum (Acari; Ixodidae): investigations into the scototaxis of unfed adult ticks

Under controlled test conditions, unfed male and female Hyalomma truncatum ticks exhibited a positive scototaxis to stationary, two-dimensional targets. Upright-positioned rectangles were the most attractive targets. The attractiveness of these targets increased with their size. Significantly more ticks responded scototactically positively to the targets under a luminance contrast ratio of 5:1, as compared with other luminance contrast ratios. Targets with an elevation angle of 13 degrees were occupied more frequently than objects with higher elevation angles. Scototaxis was the same towards a stationary and a sinusoid oscillating target. When an upright-positioned rectangle was combined with a CO2 gradient, the number of ticks that migrated into the CO2 gradient and contacted the target did not increase significantly. The interval between exposure and first locomotion of the ticks, however, was significantly shorter under the influence of a CO2 gradient than in all other experiments without a CO2 gradient. A temperature gradient simulating a natural host (cattle) did not alter the scototaxis. The results of these investigations suggest that the positive scototaxis exhibited by adult H. truncatum ticks is not likely to be part of their appetence behaviour but rather searching behaviour to find adequate protection from harsh climatic conditions.

Target course recognition using nonsinusoidal look-down radars

The target signature of an airplane as viewed by a nonsinusoidal look-down radar is obtained analytically as a function of target shape, azimuth orientation, look-down angle, and transmitted pulse duration. The information contained in the target signature can be used for detection of stationary and moving targets in heavy clutter, as well as the recognition of target shape and orientation. The relation between target signature and target azimuth orientation shows that pulse lengths shorter than airplane length are required to perform target recognition at all azimuth angles. Target course recognition in the radar ground plane is the process of determining the azimuth angle by selecting from the database the target signature that is most similar to the observed one. The effect of look-down angle on the target signature is also analyzed. At small look-down angles, target shape information is obtained with pulse lengths shorter than aircraft length. However, at large look-down angles pulse lengths much shorter than the airplane length are required. The variation of the target signature with azimuth and look-down angles are utilized for determining two-dimensional target course recognition. Cruise missile radars operating in a lookdown mode can utilize the very-high-resolution nonsinusoidal radar to enhance target shape recognition in addition to target course recognition.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Two-dimensional model of ion dynamics during plasma source ion implantation

Ion dynamics in the plasma sheath following the application of a negative voltage pulse to a two-dimensional target are modeled using a time-dependent, two-fluid simulation. The target considered is a square bar of infinite length. We find that the sheath focuses ions near to, but not on, the corner of the bar, resulting in an enhancement of the dose received there.

Two-dimensional QCD is a string theory

The partition function of two-dimensional QCD on a Riemann surface of area A is expanded as a power series in 1 N and A . It is shown that the coefficients of this expansion are precisely determined by a sum over maps from a two-dimensional surface onto the two-dimensional target space. Thus two-dimensional QCD has a simple interpretation as a closed string theory.