Tobias Roths - Academia.edu (original) (raw)
Papers by Tobias Roths
Proceedings of SPIE, Mar 15, 2004
The determination of optical properties of turbid, absorbing media is of increasing interest in b... more The determination of optical properties of turbid, absorbing media is of increasing interest in both reseach and industry. In order to estimate the optical properties from steady-state diffuse reflectance measurements sophisticaed analytical models have been introduced. These models, which are based on diffusion approximation, properly explain the diffuse reflectance of low absorbing media in the so-called asymptotic region, which means
International Journal Of Legal Medicine, Apr 21, 2005
In terms of physics, the skin can be regarded as an optically turbid medium in which the light is... more In terms of physics, the skin can be regarded as an optically turbid medium in which the light is mainly scattered by the collagen fibers, mitochondria and cell nuclei, whereas the absorption is determined by the content of reduced hemoglobin, oxyhemoglobin, bilirubin, and melanin. When the measuring geometry and the illumination spectrum are known, the optical characteristics of the skin can be approximately described by the diffusion and absorption coefficients. These values define the diffusion and absorption probability per unit distance traveled for each wavelength. Based on these parameters, a mathematical skin model was developed with the help of Monte Carlo simulations. By implementing the absorption coefficient of carbon monoxide hemoglobin (CO-Hb) into the skin model, the authors wanted to investigate whether this method is suitable to determine the CO-Hb concentration from spectral reflectance curves of livores. The investigations performed on 28 deaths from CO poisoning so far showed that this is generally possible. In almost all cases, the actual CO-Hb values could be estimated correctly by using the Monte Carlo simulations.
Physical review, Sep 24, 2001
Dynamic light scattering experiments have become a powerful tool in order to investigate the dyna... more Dynamic light scattering experiments have become a powerful tool in order to investigate the dynamical properties of complex fluids. In many applications in both soft matter research and industry so-called "real world" systems are subject of great interest. Here, the dilution of the investigated system often cannot be changed without getting measurement artifacts, so that one often has to deal with highly concentrated and turbid media. The investigation of such systems requires techniques that suppress the influence of multiple scattering, e.g., cross correlation techniques. However, measurements at turbid as well as highly diluted media lead to data with low signal-to-noise ratio, which complicates data analysis and leads to unreliable results. In this article a multiangle regularization method is discussed, which copes with the difficulties arising from such samples and enhances enormously the quality of the estimated solution. In order to demonstrate the efficiency of this multiangle regularization method we applied it to cross correlation functions measured at highly turbid samples.
The material properties of heterogeneous polymer blends are crucially influenced by their morphol... more The material properties of heterogeneous polymer blends are crucially influenced by their morphology, i.e. by the spatial structure of the blend components. In order to understand the experimentally resulting morphologies, the dynamics of the morphology formation have to be modeled. The discussed model consists of a system of partial differential equations based on a modified Cahn-Hilliard equation, the continuity equation, and a modified Navier-Stokes equation. It includes the essential material and processing parameters like surface tension, viscosity and volume fraction of both polymers, and imposed shear rate. For the simulation of a two dimensional model a numerical algorithm was developed. Simulations show a variety of morphologies in dependence on the processing parameters that qualitatively correspond to experimental results.
Progress and Trends in Rheology V, 1998
ABSTRACT
Bildverarbeitung Fur Die Medizin, 1996
Eprint Arxiv Cond Mat 0009169, Sep 12, 2000
This is the last part of a series of five articles published in Journal of Rheology (Maier et al.... more This is the last part of a series of five articles published in Journal of Rheology (Maier et al. (1998), Thimm et al. (1999a), Thimm et al. (2000a), Thimm et al. (2000c)) in which progress on the determination of binary molecular weight distributions from rheological data has been reported. In this article is discussed in how far the developed methods can also be used to characterize long-chain branching effects. Monomodal samples which contain long-chain branches will show two relaxation processes in the rheological examination, which are converted to two peaks in a corresponding molecular weight distribution. But these samples will show only one peak in a molecular weight distribution determined by a size-exclusion chromatography examination. This difference can be used to characterize long-chain branched materials as will be explained in this article. The usefulness of this method is demonstrated by examining polymers, which contain definite long-chain branches specified from the way, they were made.
Smart Medical and Biomedical Sensor Technology, 2004
The determination of optical properties of turbid, absorbing media is of increasing interest in b... more The determination of optical properties of turbid, absorbing media is of increasing interest in both reseach and industry. In order to estimate the optical properties from steady-state diffuse reflectance measurements sophisticaed analytical models have been introduced. These models, which are based on diffusion approximation, properly explain the diffuse reflectance of low absorbing media in the so-called asymptotic region, which means
Physical review. E, Statistical, nonlinear, and soft matter physics, 2001
Dynamic light scattering experiments have become a powerful tool in order to investigate the dyna... more Dynamic light scattering experiments have become a powerful tool in order to investigate the dynamical properties of complex fluids. In many applications in both soft matter research and industry so-called "real world" systems are subject of great interest. Here, the dilution of the investigated system often cannot be changed without getting measurement artifacts, so that one often has to deal with highly concentrated and turbid media. The investigation of such systems requires techniques that suppress the influence of multiple scattering, e.g., cross correlation techniques. However, measurements at turbid as well as highly diluted media lead to data with low signal-to-noise ratio, which complicates data analysis and leads to unreliable results. In this article a multiangle regularization method is discussed, which copes with the difficulties arising from such samples and enhances enormously the quality of the estimated solution. In order to demonstrate the efficiency of t...
This is the last part of a series of five articles published in Journal of Rheology (Maier et al.... more This is the last part of a series of five articles published in Journal of Rheology (Maier et al. (1998), Thimm et al. (1999a), Thimm et al. (2000a), Thimm et al. (2000c)) in which progress on the determination of binary molecular weight distributions from rheological data has been reported. In this article is discussed in how far the developed methods
Macromolecular Symposia, 2000
ABSTRACT
Journal of Rheology, 2000
In this article a model is proposed for the kernel in the generalized mixing rule recently formul... more In this article a model is proposed for the kernel in the generalized mixing rule recently formulated by Anderssen and Mead [Anderssen, RS and DW Mead, J. Non-Newtonian Fluid Mech.[bold 76], 299–306 (1998)]. In order to derive such a model, it is necessary to take ...
International Journal of Legal Medicine, 2005
In terms of physics, the skin can be regarded as an optically turbid medium in which the light is... more In terms of physics, the skin can be regarded as an optically turbid medium in which the light is mainly scattered by the collagen fibers, mitochondria and cell nuclei, whereas the absorption is determined by the content of reduced hemoglobin, oxyhemoglobin, bilirubin, and melanin. When the measuring geometry and the illumination spectrum are known, the optical characteristics of the skin can be approximately described by the diffusion and absorption coefficients. These values define the diffusion and absorption probability per unit distance traveled for each wavelength. Based on these parameters, a mathematical skin model was developed with the help of Monte Carlo simulations. By implementing the absorption coefficient of carbon monoxide hemoglobin (CO-Hb) into the skin model, the authors wanted to investigate whether this method is suitable to determine the CO-Hb concentration from spectral reflectance curves of livores. The investigations performed on 28 deaths from CO poisoning so far showed that this is generally possible. In almost all cases, the actual CO-Hb values could be estimated correctly by using the Monte Carlo simulations.
Computer Physics Communications, 2001
In many fields of science one is interested in functions which are not directly accessible by exp... more In many fields of science one is interested in functions which are not directly accessible by experiment but have to inferred from an experimentally measurable quantity by solving an inverse problem. In general, this constitutes an ill-posed problem. Therefore so-called regularization methods are necessary: Besides the constraint from the experimental data these methods impose additional information on the solution, denoted as prior information and modeled by the so-called regularization term. For example, the Tikhonov regularization respectively its generalization to nonlinear inverse problems, denoted as nonlinear regularization method and implemented in the program NLREG (J. Weese, Comput. Phys. Commun. 77 (1993) 429), are based on the prior information that the solution is smooth. Thus, one is restricted to a specific linear regularization term. However, there exist some regularization methods which make use of more elaborate prior information. Accordingly, there is a need for a program that can handle more general, in particular nonlinear regularization terms. Hence, the nonlinear regularization method is generalized in order to comply with this need. This generalized nonlinear regularization method is implemented in the program GENEREG.
Proceedings of SPIE, Mar 15, 2004
The determination of optical properties of turbid, absorbing media is of increasing interest in b... more The determination of optical properties of turbid, absorbing media is of increasing interest in both reseach and industry. In order to estimate the optical properties from steady-state diffuse reflectance measurements sophisticaed analytical models have been introduced. These models, which are based on diffusion approximation, properly explain the diffuse reflectance of low absorbing media in the so-called asymptotic region, which means
International Journal Of Legal Medicine, Apr 21, 2005
In terms of physics, the skin can be regarded as an optically turbid medium in which the light is... more In terms of physics, the skin can be regarded as an optically turbid medium in which the light is mainly scattered by the collagen fibers, mitochondria and cell nuclei, whereas the absorption is determined by the content of reduced hemoglobin, oxyhemoglobin, bilirubin, and melanin. When the measuring geometry and the illumination spectrum are known, the optical characteristics of the skin can be approximately described by the diffusion and absorption coefficients. These values define the diffusion and absorption probability per unit distance traveled for each wavelength. Based on these parameters, a mathematical skin model was developed with the help of Monte Carlo simulations. By implementing the absorption coefficient of carbon monoxide hemoglobin (CO-Hb) into the skin model, the authors wanted to investigate whether this method is suitable to determine the CO-Hb concentration from spectral reflectance curves of livores. The investigations performed on 28 deaths from CO poisoning so far showed that this is generally possible. In almost all cases, the actual CO-Hb values could be estimated correctly by using the Monte Carlo simulations.
Physical review, Sep 24, 2001
Dynamic light scattering experiments have become a powerful tool in order to investigate the dyna... more Dynamic light scattering experiments have become a powerful tool in order to investigate the dynamical properties of complex fluids. In many applications in both soft matter research and industry so-called "real world" systems are subject of great interest. Here, the dilution of the investigated system often cannot be changed without getting measurement artifacts, so that one often has to deal with highly concentrated and turbid media. The investigation of such systems requires techniques that suppress the influence of multiple scattering, e.g., cross correlation techniques. However, measurements at turbid as well as highly diluted media lead to data with low signal-to-noise ratio, which complicates data analysis and leads to unreliable results. In this article a multiangle regularization method is discussed, which copes with the difficulties arising from such samples and enhances enormously the quality of the estimated solution. In order to demonstrate the efficiency of this multiangle regularization method we applied it to cross correlation functions measured at highly turbid samples.
The material properties of heterogeneous polymer blends are crucially influenced by their morphol... more The material properties of heterogeneous polymer blends are crucially influenced by their morphology, i.e. by the spatial structure of the blend components. In order to understand the experimentally resulting morphologies, the dynamics of the morphology formation have to be modeled. The discussed model consists of a system of partial differential equations based on a modified Cahn-Hilliard equation, the continuity equation, and a modified Navier-Stokes equation. It includes the essential material and processing parameters like surface tension, viscosity and volume fraction of both polymers, and imposed shear rate. For the simulation of a two dimensional model a numerical algorithm was developed. Simulations show a variety of morphologies in dependence on the processing parameters that qualitatively correspond to experimental results.
Progress and Trends in Rheology V, 1998
ABSTRACT
Bildverarbeitung Fur Die Medizin, 1996
Eprint Arxiv Cond Mat 0009169, Sep 12, 2000
This is the last part of a series of five articles published in Journal of Rheology (Maier et al.... more This is the last part of a series of five articles published in Journal of Rheology (Maier et al. (1998), Thimm et al. (1999a), Thimm et al. (2000a), Thimm et al. (2000c)) in which progress on the determination of binary molecular weight distributions from rheological data has been reported. In this article is discussed in how far the developed methods can also be used to characterize long-chain branching effects. Monomodal samples which contain long-chain branches will show two relaxation processes in the rheological examination, which are converted to two peaks in a corresponding molecular weight distribution. But these samples will show only one peak in a molecular weight distribution determined by a size-exclusion chromatography examination. This difference can be used to characterize long-chain branched materials as will be explained in this article. The usefulness of this method is demonstrated by examining polymers, which contain definite long-chain branches specified from the way, they were made.
Smart Medical and Biomedical Sensor Technology, 2004
The determination of optical properties of turbid, absorbing media is of increasing interest in b... more The determination of optical properties of turbid, absorbing media is of increasing interest in both reseach and industry. In order to estimate the optical properties from steady-state diffuse reflectance measurements sophisticaed analytical models have been introduced. These models, which are based on diffusion approximation, properly explain the diffuse reflectance of low absorbing media in the so-called asymptotic region, which means
Physical review. E, Statistical, nonlinear, and soft matter physics, 2001
Dynamic light scattering experiments have become a powerful tool in order to investigate the dyna... more Dynamic light scattering experiments have become a powerful tool in order to investigate the dynamical properties of complex fluids. In many applications in both soft matter research and industry so-called "real world" systems are subject of great interest. Here, the dilution of the investigated system often cannot be changed without getting measurement artifacts, so that one often has to deal with highly concentrated and turbid media. The investigation of such systems requires techniques that suppress the influence of multiple scattering, e.g., cross correlation techniques. However, measurements at turbid as well as highly diluted media lead to data with low signal-to-noise ratio, which complicates data analysis and leads to unreliable results. In this article a multiangle regularization method is discussed, which copes with the difficulties arising from such samples and enhances enormously the quality of the estimated solution. In order to demonstrate the efficiency of t...
This is the last part of a series of five articles published in Journal of Rheology (Maier et al.... more This is the last part of a series of five articles published in Journal of Rheology (Maier et al. (1998), Thimm et al. (1999a), Thimm et al. (2000a), Thimm et al. (2000c)) in which progress on the determination of binary molecular weight distributions from rheological data has been reported. In this article is discussed in how far the developed methods
Macromolecular Symposia, 2000
ABSTRACT
Journal of Rheology, 2000
In this article a model is proposed for the kernel in the generalized mixing rule recently formul... more In this article a model is proposed for the kernel in the generalized mixing rule recently formulated by Anderssen and Mead [Anderssen, RS and DW Mead, J. Non-Newtonian Fluid Mech.[bold 76], 299–306 (1998)]. In order to derive such a model, it is necessary to take ...
International Journal of Legal Medicine, 2005
In terms of physics, the skin can be regarded as an optically turbid medium in which the light is... more In terms of physics, the skin can be regarded as an optically turbid medium in which the light is mainly scattered by the collagen fibers, mitochondria and cell nuclei, whereas the absorption is determined by the content of reduced hemoglobin, oxyhemoglobin, bilirubin, and melanin. When the measuring geometry and the illumination spectrum are known, the optical characteristics of the skin can be approximately described by the diffusion and absorption coefficients. These values define the diffusion and absorption probability per unit distance traveled for each wavelength. Based on these parameters, a mathematical skin model was developed with the help of Monte Carlo simulations. By implementing the absorption coefficient of carbon monoxide hemoglobin (CO-Hb) into the skin model, the authors wanted to investigate whether this method is suitable to determine the CO-Hb concentration from spectral reflectance curves of livores. The investigations performed on 28 deaths from CO poisoning so far showed that this is generally possible. In almost all cases, the actual CO-Hb values could be estimated correctly by using the Monte Carlo simulations.
Computer Physics Communications, 2001
In many fields of science one is interested in functions which are not directly accessible by exp... more In many fields of science one is interested in functions which are not directly accessible by experiment but have to inferred from an experimentally measurable quantity by solving an inverse problem. In general, this constitutes an ill-posed problem. Therefore so-called regularization methods are necessary: Besides the constraint from the experimental data these methods impose additional information on the solution, denoted as prior information and modeled by the so-called regularization term. For example, the Tikhonov regularization respectively its generalization to nonlinear inverse problems, denoted as nonlinear regularization method and implemented in the program NLREG (J. Weese, Comput. Phys. Commun. 77 (1993) 429), are based on the prior information that the solution is smooth. Thus, one is restricted to a specific linear regularization term. However, there exist some regularization methods which make use of more elaborate prior information. Accordingly, there is a need for a program that can handle more general, in particular nonlinear regularization terms. Hence, the nonlinear regularization method is generalized in order to comply with this need. This generalized nonlinear regularization method is implemented in the program GENEREG.