Search results for "Inverse problem"
showing 10 items of 163 documents
A partially reflecting random walk on spheres algorithm for electrical impedance tomography
2015
In this work, we develop a probabilistic estimator for the voltage-to-current map arising in electrical impedance tomography. This novel so-called partially reflecting random walk on spheres estimator enables Monte Carlo methods to compute the voltage-to-current map in an embarrassingly parallel manner, which is an important issue with regard to the corresponding inverse problem. Our method uses the well-known random walk on spheres algorithm inside subdomains where the diffusion coefficient is constant and employs replacement techniques motivated by finite difference discretization to deal with both mixed boundary conditions and interface transmission conditions. We analyze the global bias…
An iterative method in a probabilistic approach to the spectral inverse problem - Differential emission measure from line spectra and broadband data
2010
Inverse problems are of great importance in astrophysics for deriving information about the physical characteristics of hot optically thin plasma sources from their EUV and X-ray spectra. We describe and test an iterative method developed within the framework of a probabilistic approach to the spectral inverse problem for determining the thermal structures of the emitting plasma. We also demonstrate applications of this method to both high resolution line spectra and broadband imaging data. Our so-called Bayesian iterative method (BIM) is an iterative procedure based on Bayes' theorem and is used to reconstruct differential emission measure (DEM) distributions. To demonstrate the abilities …
Inverse task for evaluation of particle size distribution of polydisperse magnetic fluids
2010
AbstractThe method of inverse task was used to analyze three different physical phenomena. The particle size distributions were reconstructed from the magnetization curve, dynamic light scattering and magnetic birefringence relaxation data. The results thus obtained for one real magnetic fluid sample are different; they characterize the physical nature of the phenomena. All three methods may be used to determine intrinsic sample properties.
Recent progress on Frequency Difference Electrical Impedance Tomography
2009
Although time-dierence EIT(tdEIT) has shown promise as a medical EIT imaging tech- nique such as monitoring lung function, static EIT has suered from forward computational model errors including boundary geometry and electrode positions uncertainty combined with the ill-posed and highly nonlinear nature of the corresponding inverse problem. Since 1980s, there has been great endeavor to create forward computational models with the necessary accuracy required for EIT recon- struction, but these eorts were not successful in clinical environment. This is the main reason why we consider frequency-dieren ce EIT (fdEIT) where we take advantage of frequency dependance of biological tissue by inject…
Inverse problem for the Landau-Zener effect
2002
We consider the inverse Landau-Zener problem which consists in finding the energy-sweep functions W(t)=E1(t)-E2(t) resulting in the required time dependences of the level populations for a two-level system crossing the resonance one or more times during the sweep. We find sweep functions of particular forms that let manipulate the system in a required way, including complete switching from the state 1 to the state 2 and preparing the system at the exact ground and excited states at resonance.
Sampling expansions for three-dimensional light amplitude distribution in the vicinity of an axial image point: comment.
2003
Landgrave and Berriel-Valdos presented axial and radial sampling expansions for three-dimensional light amplitude distribution around the Gaussian focal point. [J. Opt. Soc. Am. A 14, 2962 (1997)]. The expansions were obtained under the assumption that the pupil function was rotationally symmetric. We present a new derivation of the axial expansion that does not make use of arbitrary formal assumptions used by Landgrave and Berriel-Valdos and eliminates some faults of the derivation given by Arsenault and Boivin, who published this expansion in 1967 [J. Appl. Phys. 38, 3988 (1967)]. We also discuss generalizations of the axial expansion to the case of pupils that exhibit no symmetry with re…
Unitary chiral dynamics of two hadrons in a finite volume: theKD,ηDssystem and theDs*0(2317) resonance
2012
We investigate the KD and ηDs system in a finite volume and study the properties of the Ds*0(2317) resonance, which is generated in this coupled channel system. We calculate the energy levels in a cubic box and considering them as synthetic lattice data we solve the inverse problem of determining the bound states and phase shifts in the infinite volume. We observe that it is possible to obtain accurate KD phase shifts and the position of the Ds*0(2317) state from the synthetic lattice data considered and that a careful analysis of the finite volume data can shed some light on the nature of the Ds*0(2317) resonance as a KD molecule or otherwise.
Application of Rotational Measurements in Stiffness Reconstruction of Beams and Frames
2009
A stiffness reconstruction method is tested when rotational degrees of freedom are added to the dynamic model of the structure. The inverse problem is formulated as a minimization problem in terms of harmonic vibrations of the structure and its finite element model. An example of frame structure is analyzed by numerical simulations. The results of these numerical analyses show that the damage detection appeared to be much more effective when the angular amplitudes of harmonic vibrations are acquired. This makes very good prospects for the future applications of angular sensors in damage detection of structures.
KPZ equation with realistic short-range-correlated noise
2003
We study a realistic simulation model for the propagation of slow-combustion fronts in paper. In the simulations the deterministic part of the dynamics is that of the KPZ equation. The stochastic part, including in particular the short-range noise correlations, is taken from images of the structure of real paper samples. The parameters of the simulations are determined by using an inverse method applied to the experimental front data and by comparing the simulated and the experimental effective-noise distributions. Our model predicts well the shape of the spatial and temporal correlation functions, including the location of the crossovers from short-range (SR) to long-range (LR) behavior. T…
Determination of the stochastic evolution equation from noisy experimental data
2003
We have determined the coefficients of the Kardar-Parisi-Zhang equation as functions of coarse graining, which best describe the time evolution and spatial behavior observed for slow-combustion fronts in sheets of paper and magnetic flux fronts in a thin-film high-Tc superconductor. Reconstruction of the relevant equation of motion and its coefficients was mainly based on the inverse method proposed by Lam and Sander [Phys. Rev. Lett. 71, 561 (1993)]. The coefficient of the nonlinear term was also determined from the local slope-dependence of the front velocity.