A deterministic model of tuberculosis in Cameroon is designed and analyzed with respect to its tr... more A deterministic model of tuberculosis in Cameroon is designed and analyzed with respect to its transmission dynamics. The model includes lack of access to treatment and weak diagnosis capacity as well as both frequency- and density-dependent transmissions. It is shown that the model is mathematically well-posed and epidemiologically reasonable. Solutions are non-negative and bounded whenever the initial values are non-negative. A sensitivity analysis of model parameters is performed and the most sensitive ones are identified by means of a state-of-the-art Gauss-Newton method. In particular, parameters representing the proportion of individuals having access to medical facilities are seen to have a large impact on the dynamics of the disease. The model predicts that a gradual increase of these parameters could significantly reduce the disease burden on the population within the next 15 years.
... (2.2.4a) [Smax] Omax with 00 as defined in (1.1.9). Further, replacing the condition number i... more ... (2.2.4a) [Smax] Omax with 00 as defined in (1.1.9). Further, replacing the condition number in (2.2.3a) by the subcondition number sc (J(s)) due to [9], leads to (2.2.4b) [ Smin]:= E sc ((sO)) )So e: selected parameter (say E = epmach). If [Smin] < So < [Smax], then so is accepted. ...
Experimental and numerical methods were used to determine the coupling of energy in a multichanne... more Experimental and numerical methods were used to determine the coupling of energy in a multichannel three-dimensional hyperthermia applicator (SIGMA-Eye), consisting of 12 short dipole antenna pairs with stubs for impedance matching. The relationship between the amplitudes and phases of the forward waves from the amplifiers, to the resulting amplitudes and phases at the antenna feed-points was determined in terms of
IEEE Antennas and Propagation Society International Symposium. 1999 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.99CH37010), 1999
The purpose of this contribution is to develop high performance short antenna structures which ca... more The purpose of this contribution is to develop high performance short antenna structures which can be used as basic array elements of the 3D phased array for hyperthermia (HT) applications in the pelvis. The numerical design of basic array elements of the 3D HT applicator has been performed in a systematic way applying the finite-difference time-domain (FDTD) method. Some modifications
Time-efficient and easy-to-use segmentation algorithms (contour generation) are a precondition fo... more Time-efficient and easy-to-use segmentation algorithms (contour generation) are a precondition for various applications in radiation oncology, especially for planning purposes in hyperthermia. We have developed the three following algorithms for contour generation and implemented them in an editor of the HyperPlan hyperthermia planning system. Firstly, a manual contour input with numerous correction and editing options. Secondly, a volume growing algorithm with adjustable threshold range and minimal region size. Thirdly, a watershed transformation in two and three dimensions. In addition, the region input function of the Helax commercial radiation therapy planning system was available for comparison. All four approaches were applied under routine conditions to two-dimensional computed tomographic slices of the superior thoracic aperture, mid-chest, upper abdomen, mid-abdomen, pelvis and thigh; they were also applied to a 3D CT sequence of 72 slices using the three-dimensional extension of the algorithms. Time to generate the contours and their quality with respect to a reference model were determined. Manual input for a complete patient model required approximately 5 to 6 h for 72 CT slices (4.5 min/slice). If slight irregularities at object boundaries are accepted, this time can be reduced to 3.5 min/slice using the volume growing algorithm. However, generating a tetrahedron mesh from such a contour sequence for hyperthermia planning (the basis for finite-element algorithms) requires a significant amount of postediting. With the watershed algorithm extended to three dimensions, processing time can be further reduced to 3 min/slice while achieving satisfactory contour quality. Therefore, this method is currently regarded as offering some potential for efficient automated model generation in hyperthermia. In summary, the 3D volume growing algorithm and watershed transformation are both suitable for segmentation of even low-contrast objects. However, they are not always superior to user-friendly manual programs for contour generation. When the volume growing algorithm is used, the contours have to be postprocessed with suitable filters. The watershed transformation has a large potential if appropriately developed to 3D sequences and 3D interaction features. After all, the practicality and feasibility of every segmentation method critically depend on various details of the user software as pointed out in this article.
This book presents papers on large scale scientific computing. It includes: Initial value problem... more This book presents papers on large scale scientific computing. It includes: Initial value problems of ODE's and parabolic PDE's; Boundary value problems of ODE's and elliptic PDE's; Hyperbolic PDE's; Inverse problems; Optimization and optimal control problems; and Algorithm adaptation on supercomputers.
IEEE Transactions on Antennas and Propagation, 2003
A general integral finite-difference time-domain (FDTD) formulation on cubical grids for the mode... more A general integral finite-difference time-domain (FDTD) formulation on cubical grids for the modeling of electrically inhomogeneous media of arbitrary shape is derived. The simple cubical structure is maintained and no modifications of the integral paths are necessary. Instead, a three-dimensional tensor relationship between the average electric flux density and electric field is determined beforehand and used during the simulation to
IEEE Transactions on Antennas and Propagation, 2003
A general and consistent integral finite-difference time-domain (FDTD) formulation on cubical gri... more A general and consistent integral finite-difference time-domain (FDTD) formulation on cubical grids for modeling of cylindrical antennas with or without dielectric coating is derived. No additional grid points or modifications of the integral paths are necessary. Instead, effective material properties are modified in the FDTD grid. Thus, even for insulated antennas, the simple cubical structure is maintained. Special integral factors
Page 1. Discrete transparent boundary conditions for the Schrödinger equation on circular domains... more Page 1. Discrete transparent boundary conditions for the Schrödinger equation on circular domains Anton Arnold1, Matthias Ehrhardt2, Maike Schulte3, Ivan Sofronov4 anton.arnold@tuwien.ac.at, ehrhardt@wias-berlin.de, Maike ...
A deterministic model of tuberculosis in Cameroon is designed and analyzed with respect to its tr... more A deterministic model of tuberculosis in Cameroon is designed and analyzed with respect to its transmission dynamics. The model includes lack of access to treatment and weak diagnosis capacity as well as both frequency- and density-dependent transmissions. It is shown that the model is mathematically well-posed and epidemiologically reasonable. Solutions are non-negative and bounded whenever the initial values are non-negative. A sensitivity analysis of model parameters is performed and the most sensitive ones are identified by means of a state-of-the-art Gauss-Newton method. In particular, parameters representing the proportion of individuals having access to medical facilities are seen to have a large impact on the dynamics of the disease. The model predicts that a gradual increase of these parameters could significantly reduce the disease burden on the population within the next 15 years.
... (2.2.4a) [Smax] Omax with 00 as defined in (1.1.9). Further, replacing the condition number i... more ... (2.2.4a) [Smax] Omax with 00 as defined in (1.1.9). Further, replacing the condition number in (2.2.3a) by the subcondition number sc (J(s)) due to [9], leads to (2.2.4b) [ Smin]:= E sc ((sO)) )So e: selected parameter (say E = epmach). If [Smin] < So < [Smax], then so is accepted. ...
Experimental and numerical methods were used to determine the coupling of energy in a multichanne... more Experimental and numerical methods were used to determine the coupling of energy in a multichannel three-dimensional hyperthermia applicator (SIGMA-Eye), consisting of 12 short dipole antenna pairs with stubs for impedance matching. The relationship between the amplitudes and phases of the forward waves from the amplifiers, to the resulting amplitudes and phases at the antenna feed-points was determined in terms of
IEEE Antennas and Propagation Society International Symposium. 1999 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.99CH37010), 1999
The purpose of this contribution is to develop high performance short antenna structures which ca... more The purpose of this contribution is to develop high performance short antenna structures which can be used as basic array elements of the 3D phased array for hyperthermia (HT) applications in the pelvis. The numerical design of basic array elements of the 3D HT applicator has been performed in a systematic way applying the finite-difference time-domain (FDTD) method. Some modifications
Time-efficient and easy-to-use segmentation algorithms (contour generation) are a precondition fo... more Time-efficient and easy-to-use segmentation algorithms (contour generation) are a precondition for various applications in radiation oncology, especially for planning purposes in hyperthermia. We have developed the three following algorithms for contour generation and implemented them in an editor of the HyperPlan hyperthermia planning system. Firstly, a manual contour input with numerous correction and editing options. Secondly, a volume growing algorithm with adjustable threshold range and minimal region size. Thirdly, a watershed transformation in two and three dimensions. In addition, the region input function of the Helax commercial radiation therapy planning system was available for comparison. All four approaches were applied under routine conditions to two-dimensional computed tomographic slices of the superior thoracic aperture, mid-chest, upper abdomen, mid-abdomen, pelvis and thigh; they were also applied to a 3D CT sequence of 72 slices using the three-dimensional extension of the algorithms. Time to generate the contours and their quality with respect to a reference model were determined. Manual input for a complete patient model required approximately 5 to 6 h for 72 CT slices (4.5 min/slice). If slight irregularities at object boundaries are accepted, this time can be reduced to 3.5 min/slice using the volume growing algorithm. However, generating a tetrahedron mesh from such a contour sequence for hyperthermia planning (the basis for finite-element algorithms) requires a significant amount of postediting. With the watershed algorithm extended to three dimensions, processing time can be further reduced to 3 min/slice while achieving satisfactory contour quality. Therefore, this method is currently regarded as offering some potential for efficient automated model generation in hyperthermia. In summary, the 3D volume growing algorithm and watershed transformation are both suitable for segmentation of even low-contrast objects. However, they are not always superior to user-friendly manual programs for contour generation. When the volume growing algorithm is used, the contours have to be postprocessed with suitable filters. The watershed transformation has a large potential if appropriately developed to 3D sequences and 3D interaction features. After all, the practicality and feasibility of every segmentation method critically depend on various details of the user software as pointed out in this article.
This book presents papers on large scale scientific computing. It includes: Initial value problem... more This book presents papers on large scale scientific computing. It includes: Initial value problems of ODE's and parabolic PDE's; Boundary value problems of ODE's and elliptic PDE's; Hyperbolic PDE's; Inverse problems; Optimization and optimal control problems; and Algorithm adaptation on supercomputers.
IEEE Transactions on Antennas and Propagation, 2003
A general integral finite-difference time-domain (FDTD) formulation on cubical grids for the mode... more A general integral finite-difference time-domain (FDTD) formulation on cubical grids for the modeling of electrically inhomogeneous media of arbitrary shape is derived. The simple cubical structure is maintained and no modifications of the integral paths are necessary. Instead, a three-dimensional tensor relationship between the average electric flux density and electric field is determined beforehand and used during the simulation to
IEEE Transactions on Antennas and Propagation, 2003
A general and consistent integral finite-difference time-domain (FDTD) formulation on cubical gri... more A general and consistent integral finite-difference time-domain (FDTD) formulation on cubical grids for modeling of cylindrical antennas with or without dielectric coating is derived. No additional grid points or modifications of the integral paths are necessary. Instead, effective material properties are modified in the FDTD grid. Thus, even for insulated antennas, the simple cubical structure is maintained. Special integral factors
Page 1. Discrete transparent boundary conditions for the Schrödinger equation on circular domains... more Page 1. Discrete transparent boundary conditions for the Schrödinger equation on circular domains Anton Arnold1, Matthias Ehrhardt2, Maike Schulte3, Ivan Sofronov4 anton.arnold@tuwien.ac.at, ehrhardt@wias-berlin.de, Maike ...
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