Quasi-analytic Method Research Articles

Model-Based VF Technique for Parasitic Reflections Reduction of Frequency-Domain Chipless RFID Systems

In a frequency-domain chipless RFID system, the backscattered signal from a tag is directly obtained in the frequency domain over limited bandwidth. However, to reduce the parasitic reflections, it is crucial to obtain the backscattered signal in the time domain. This letter proposes a precise quasi-analytic method, known as the model-based vector fitting (VF) technique, to provide the closed-form equation of the backscattered response in the time domain. The proposed method successfully recovers a tag’s identification (ID) among parasitic reflections using a single tag measurement without requiring prior knowledge about the tag.

2π ambiguity-free digital holography method forstepped phase imaging.

It is known that phase ambiguity is always an inherent problem in digital holography. In this paper, a 2π ambiguity-free digital holography method is proposed. The method naturally avoids phase ambiguity by a quasianalytic method. This quasianalytic method accurately calculates the true phase by constructing an equation and solving the solution of the equation. Thus, the inherent wrapping problem in digital holography is eliminated. For example, our experimental result shows that the true phase of the stepped specimen with the phase distributed in [0, 16π] can be obtained unambiguously. Since the proposed method naturally avoids the phase ambiguity problem, it may be beneficial to enlarge the application potential of the digital holography. The effectiveness and accuracy of the proposed method are verified by both numerical simulations and experimental results.

Real-Option Valuation in Multiple Dimensions Using Poisson Optional Stopping Times

We provide a new framework for valuing multidimensional real options where opportunities to exercise the option are generated by an exogenous Poisson process, which can be viewed as a liquidity constraint on decision times. This approach, which we call the Poisson optional stopping times (POST) method, finds the value function as a monotone sequence of lower bounds. In a case study, we demonstrate that the frequently used quasi-analytic method yields a suboptimal policy and an inaccurate value function. The proposed method is demonstrably correct, straightforward to implement, reliable in computation, and broadly applicable in analyzing multidimensional option-valuation problems.

A generalized Grad-Shafranov equation with plasma flow under a conformal coordinate transformation

We employ a conformal mapping transformation to solve a generalized Grad-Shafranov equation with incompressible plasma flow of arbitrary direction and construct particular up-down asymmetric D-shaped and diverted tokamak equilibria. The proposed method can also be employed as an alternative quasi-analytic method to solving two dimensional elliptic partial differential equations.

Fast, deterministic computation of irradiance values using a single extended source in 3D.

Presented is a quasi-analytic method for irradiance evaluation through a single refractive surface from a single Lambertian source. The method is compared to Monte-Carlo raytracing for a sample system, producing in much less time an irradiance distribution equal to within the latter's statistical noise. In addition to its interest to optical analysis, the method is also useful for optical design problems by allowing for fast, noise-free evaluation of merit functions, along with their derivatives.

DETERMINATION OF EXTERNAL IRRADIATION FROM SOURCES WITH COMPLEX GEOMETRY CONTAINING RADIOACTIVE WASTE

A combined technique using both Monte-Carlo and quasi-analytic method has been developed for calculation of irradiation from complex objects containing radioactive waste. Monte Carlo method is used to calculate spectral, angular and spatial distributions of γ-quanta close to one of the surfaces of the concrete cask loaded with containers filled with radioactive waste (RW). Radiation characteristics at the prescribed distance are determined by integrating the point sources with calculated distributions over thissurface. Summation of photons of external radiation from individual RW isotopes allows finding the photon flux for any storage time. Application of the technique allows to calculate asymmetric loading of casks with containers filled with RW of different activity and to optimize the arrangement of the casks in the RW storage area. This allows reducing the effect of radiation-absorbed dose on the service personnel and on the areas surrounding RW storage.

The response of superpressure balloons to gravity wave motions

Abstract. Superpressure balloons (SPB), which float on constant density (isopycnic) surfaces, provide a unique way of measuring the properties of atmospheric gravity waves (GW) as a function of wave intrinsic frequency. Here we devise a quasi-analytic method of investigating the SPB response to GW motions. It is shown that the results agree well with more rigorous numerical simulations of balloon motions and provide a better understanding of the response of SPB to GW, especially at high frequencies. The methodology is applied to ascertain the accuracy of GW studies using 12 m diameter SPB deployed in the 2010 Concordiasi campaign in the Antarctic. In comparison with the situation in earlier campaigns, the vertical displacements of the SPB were measured directly using GPS. It is shown using a large number of Monte Carlo-type simulations with realistic instrumental noise that important wave parameters, such as momentum flux, phase speed and wavelengths, can be retrieved with good accuracy from SPB observations for intrinsic wave periods greater than ca. 10 min. The noise floor for momentum flux is estimated to be ca. 10−4 mPa.

Electronic Components Thermal Stability Analysis of PCB Plate Based on the Micro Unit Heat Balance Method

In the thermal stability analysis of electronic equipment, usually we obtain the temperature by quasi circuit method and analytic method. Quasi circuit method is to use the method of circuit analysis, and the heat flux in electronic equipment is simulated into current value in short circuit analysis. The temperature is simulated into a voltage of the circuit. The values of conductance and resistance are simulated into some other valued of circuit components. Analytical method is set space function subordinate relationship value of temperature in electronic equipment. Usually these two methods are desirable, but in the actual design, due to the large computational quantity of quasi circuit method and analytic method, the calculation is complex. Therefore, we combine these methods to solve some traditional disadvantages using micro unit heat balance method, which provides a new method for optimal portfolio.

A novel quasi-analytic method for transient analysis of a reflector illuminated by a corrugated horn for IRA applications

A novel quasi-analytic method for transient analysis of a reflector antenna illuminated by a corrugated horn for impulse-radiating-antenna applications is presented in this paper. Based on time-domain Gaussian beam (TD-GB) approach, the proposed method is highly efficient, independent of reflector’s size and can avoid ray-caustic problem in the ray-tracing method. The time-domain field radiated by the corrugated horn is expanded in terms of TD-GBs by matching its far-field patterns in the frequency domain (FD). TD-GB approach is utilized to investigate impulse responses. Convolution theorem and superposition theorem are adopted to achieve transient responses. In addition, fast Fourier transform of transient responses are compared with direct FD results, and good agreement is achieved.

An Improved Quasi-Analytic Method for Direct Impulse Response Analysis of an Offset Reflector

For impulse-radiating-antenna applications, an improved quasi-analytic method of offset reflectors' direct impulse response analysis is presented in this article. The offset reflector is illuminated by a time-domain Gaussian beam. The proposed method can eliminate errors caused by numerical differentiation because the numerical differentiation of step response is avoided. Time-domain physical optic approximation is utilized to investigate the direct impulse response. With the appropriate coordinate transform, the direct impulse response integral problem can be reduced to one-dimensional angular integral, which is independent of the reflector's size. Adaptive interpolation is adopted when the impulse response changes rapidly.

Stochastic gravitational wave background originating from halo mergers

The stochastic gravitational wave background (GWB) from halo mergers is investigated by a quasi-analytic method. The method we employ consists of two steps. The first step is to construct a merger tree by using the Extended Press-Schechter formalism or the Sheth & Tormen formalism, with Monte-Carlo realizations. This merger tree provides evolution of halo masses. From $N$-body simulation of two-halo mergers, we can estimate the amount of gravitational wave emission induced by the individual merger process. Therefore the second step is to combine this gravitaional wave emission to the merger tree and obtain the amplitude of GWB. We find $\Omega_{GW}\sim 10^{-19}$ for $f\sim 10^{-17}-10^{-16}$ Hz, where $\Omega_{GW}$ is the energy density of the GWB. It turns out that most of the contribution on the GWB comes from halos with masses below $10^{15} M_\odot$ and mergers at low redshift, i.e., $0<z<0.8$.

AN IMPROVED TRANSIENT QUASI-ANALYSIS METHOD FOR OFFSET REFLECTOR IN IMPULSE RADIATING ANTENNA APPLICATIONS

A transient quasi-analytic method is improved to analyze the ofiset re∞ector for impulse radiating antenna (IRA) applications. Physical optic (PO) approximation and analytic time transform (ATT) are utilized to investigate the time domain (TD) radiating characteristics of the ofiset re∞ector. With the appropriate coordinate transformation, the TD far-fleld integral problem can be simplifled to one dimensional angular integral which is independent of the re∞ector's size. In addition, the Fast Fourier Transform (FFT) of impulse responses is compared to the direct frequency domain result, and good agreement is obtained.

Adhesive contact to a coated elastic substrate

We show how the quasi-analytic method developed to solve linear elastic contacts to coated substrates (Perriot and Barthel 2004 J. Mater. Res. 19 600) may be extended to adhesive contacts. Substrate inhomogeneity lifts accidental degeneracies and highlights the general structure of the adhesive contact theory. We explain the variation of the contact variables due to substrate inhomogeneity. The relation to other approaches based on finite element analysis is discussed.

Quasi-analytic formalism for mode characteristics in highly overmoded rectangular dielectric waveguide bends

A fast and simple quasi-analytic method to simulate mode characteristics in highly overmoded rectangular dielectric waveguide bends is presented. Fast mode-based bend models are necessary, since overmoded rectangular waveguides have become very popular in optical interconnects on printed circuit boards. The proposed method combines a simple mode solver with the formalism that was proposed by Melloni et al. [J. Lightwave Technol. 16, 571 (2001)], yielding to a very convenient and accurate quasi-analytic formalism for the bend transfer function based on matrix notation. For that purpose, a simple method to approximate leaky modes is introduced. The model offers the ability to predict individual modal phases and amplitudes within a given bend as well as the calculation of coupling losses and was validated using three-dimensional beam-propagation-method simulation software.

An Iterative Method for Computing Carrier Distribution in 2-D Carrier Controlled Optical Guides

A convenient, iterative method for determining injection current generated two-dimensional carrier distributions, and consequent control of refractive index profiles, in optical guided-wave devices is presented. This method is "user-friendly" and readily adaptable to a large variety of materials and geometries. It is particularly useful for a quick and quite accurate assessment of the feasibility of operation of novel device structures. Results obtained by this quasianalytic method are shown to agree very favorably with those obtained from more general but far more complicated commercially available software.

Theoretical studies of the surface phonon linewidth

A brief review of two theoretical methods for calculating thelinewidth of surface phonons is presented with specificapplication to the low-Miller-index surfaces of Ag, Cu, and Al. In the quasi-analytic method, linewidths are calculated bytreating the cubic term of a reliable interatomic potential infirst-order, time-dependent perturbation theory. In moleculardynamics (MD) simulations, linewidths are obtained from appropriatecorrelation functions and include the fully anharmoniccontribution of the interaction potential. Surface relaxationsand phonon frequencies calculated in the harmonic approximation,using selected many-body interatomic potentials, are found to bein good agreement with results from experimental data and ab initio calculations. At 300 K, the surface phonon linewidthsrange approximately between 1 and 0.1 THz, and are found tobe in reasonable agreement with the values deduced fromexperiments. Some disagreement is found between results fromperturbative methods and MD simulations. For the low-Miller-index surfaces of Ni, available results from MD simulations also summarized.

A quasi‐analytic method for structural optimization

In the present paper, a quasi-analytic method for solving structural optimization problems has been developed by co-ordinated use of mathematical transformations, high-quality approximation and a two-level approximation strategy. The method which has the advantages of both generality in applications and high efficiency in computations is especially of benefit to large practical design problems. Several typical examples of different sorts have been optimized to test its power. © 1998 John Wiley & Sons, Ltd.

A quasi-analytic method for structural optimization

In the present paper, a quasi-analytic method for solving structural optimization problems has been developed by co-ordinated use of mathematical transformations, high-quality approximation and a two-level approximation strategy. The method which has the advantages of both generality in applications and high efficiency in computations is especially of benefit to large practical design problems. Several typical examples of different sorts have been optimized to test its power. © 1998 John Wiley & Sons, Ltd.

Streamlining Monte Carlo Simulation with the Quasi-Analytic Method

Trading strategies and contingent claims with path-dependent returns are difficult to model analytically. Monte Carlo simulation, the standard solution technique, is computationally expensive and provides a solution only for the specific parameter values used in the simulation. We present an alternative "quasi-analytic" procedure that combines the power and flexibility of the simulation approach with the computational efficiency of an analytical solution. Our method uses simulation results to construct an analytic function that provides an approximate mapping from the input parameters to the returns distribution function. This analytic function can then be used to estimate the returns distribution for other parameter values directly without further simulation. We illustrate the approach by analyzing the performance of a path-dependent long-term protective put strategy that requires rolling over a series of short-term options. The returns to the strategy depend on the investor's choice of put strike and rollover policy. We use our method to examine a risk-averse investor's optimal trading strategy, a problem that is time-consuming using standard Monte Carlo simulation. In one example, the simulation approach takes more than forty-five minutes to solve for just one particular volatility scenario, while our method provides the answer in a matter of seconds.

Turbulent free-surface flow over sills

An quasi-analytic method is presented for the calculation of free-surface flow over sills (e.g. dams under construction). Starting point is the set of shallow-water equations (SWE) valid for quasi-uniform flow. To make these equations also valid for flow over sills, adaptations to the SWE are proposed, introducing coefficients in the convection, pressure and friction terms. These terms are derived from analytical and numerical calculations with an experimental check.