Jorge A Horas - Academia.edu (original) (raw)
Papers by Jorge A Horas
J Phys a Math Gen, 1998
We consider a fully connected Hopfield-like neural network as a set of N independent perceptrons.... more We consider a fully connected Hopfield-like neural network as a set of N independent perceptrons. We trained these perceptrons using the so-called inverse perceptron rule, obtaining a matrix of synaptic couplings, that make a number of spurious states unstable. We numerically determine the optimum number of spurious states, obtained by random shooting, that must be destabilized in order to obtain an improvement in performance. The unlearning procedure generated, is shown to be able to give a high-performance associative memory characterized by: (1) an enhancement in storaging capacity; (2) an enlargement in the size of attraction basins; (3) a reduction in the number of spurious attractors and (4) a reliable and fast retrieval.
Se trata de responder bajo qué condiciones se cumple la convergencia a la distribución de Poisson... more Se trata de responder bajo qué condiciones se cumple la convergencia a la distribución de Poisson, para células tumorales sometidas a tratamientos radiobiológicos fraccionados, utilizando varias formas de administración de la dosis. Para ello también se comparan modelos que dan la probabilidad de control tumoral (TCP) usando datos experimentales obtenidos de la bibliografía. Se usan dos líneas celulares que crecen como megacolonias in vitro, las cuales son irradiadas con diversos esquemas de fraccionamiento: convencional y acelerado. Se concluye sobre las hipótesis fundamentales de los modelos utilizados y se obtiene información sobre los parámetros de cada modelo y la validez de los procesos que involucran. Se estudian, entre otros, la recuperación celular total o parcial, el efecto de la resensitización y de la repoblación celular producidos entre fracciones en ambos tipos de fraccionamiento. Se consideran los límites generalmente utilizados en mediciones de fracción de sobrevida y se analiza la validez de la aproximación de Poisson en cada caso.
Se considera la heterogeneidad de la población celular de un tumor cancerígeno. Tal heterogeneida... more Se considera la heterogeneidad de la población celular de un tumor cancerígeno. Tal heterogeneidad se manifiesta claramente en su respuesta a la radiación, produciendo que la radiocurabilidad esté determinada por las células más resistentes. Para evaluar la probabilidad de cura tumoral es determinante encontrar el correcto número de células clonogénicas, que también acusan heterogeneidad, la cual es modelada utilizando la estadística de Poisson con modelos de dos compartimientos. Se analiza también otro tipo de modelos para obtener la probabilidad de cura tumoral. En todos los casos el objetivo es determinar el correcto número de células clonogénicas, o sea, aquellas capaces de reproducir el tumor. También se considera el estado de oxigenación en el que se encuentran. Los resultados se comparan con datos experimentales de esferoides celulares de diversos tamaños. Estos sistemas in vitro son muy usados como sistema modelo en radioterapia. Palabras claves: probabilidad de control tumoral, células clonogénicas, hipoxia.
In this paper we compare different models for the tumor control probability (TCP ) using experime... more In this paper we compare different models for the tumor control probability (TCP ) using experimental data obtained from bibliography. Two cellular lines growing like megacolon ies in vitro are used and irradiated with different fractionation schemes: conventional and accelerated. We obtain conclusions on the fundamental hypothesis of each model and its usefulness for different types of division into fractions of the dosis. We obtain information about the parameters of each model and the validity of the involved processes. The following mechanisms are considered: total or partial cell recovery due to sub-lethal damages, the effect of resensitization and the cellular repopulation produced in fractions in both types of division into fractions.
Se utiliza un modelo de dos compartimientos para predecir la probabilidad de cura tumoral (TCP) e... more Se utiliza un modelo de dos compartimientos para predecir la probabilidad de cura tumoral (TCP) en esferoides celulares irradiados. Usando este modelo es posible determinar los parámetros de radiosensibil idad efectiva, considerando una distribución tipo mezcla gausiana para dichos parámetros. Con estos y aplicando la estadística de Poisson se obtiene una expresión para la probabilidad de cura tumoral. Se estudia el efecto de la radiación sobre las células en estado hipóxico (radioresistentes) y sobre aquellas en estado óxico (Menos radioresistentes). El análisis se cen tra en verificar que la curva de TCP es determinada por las células clonogénicas de mayor resistencia a la radiación. El modelo se aplica a esferoides celulares (MCTS) de distinto tamaño de una línea celular de adenocarcinoma de colon (Widr), obteniéndose interesantes correlaciones. La variación de la densidad de células clonogénicas y otros aspectos en el interior del esferoide son también considerados. A two-compar...
The delay time or time lag, i.e. the time to reach the stationary state, represents, all together... more The delay time or time lag, i.e. the time to reach the stationary state, represents, all together with the permeation, the dinamics of the diffusive process, and is of large use and usefulness to characterize the mass transport through polymeric films. Is important because is a measure of the difusive dinamics, and also because it depends on sorption equilibrium. We
Physics in Medicine and Biology, 2005
We model the heterogeneous response to radiation of multicellular tumour spheroids assuming posit... more We model the heterogeneous response to radiation of multicellular tumour spheroids assuming position- and volume-dependent radiosensitivity. We propose a method to calculate the overall radiosensitivity parameters to obtain the surviving fraction of tumours. A mathematical model of a spherical tumour with a hypoxic core and a viable rim which is a caricature of a real tumour is constructed. The model is embedded in a two-compartment linear-quadratic (LQ) model, assuming a mixed bivariated Gaussian distribution to attain the radiosensitivity parameters. Ergodicity, i.e., the equivalence between ensemble and volumetric averages is used to obtain the overall radiosensitivities for the two compartments. We obtain expressions for the overall radiosensitivity parameters resulting from the use of both a linear and a nonlinear dependence of the local radiosensitivity with position. The model's results are compared with experimental data of surviving fraction (SF) for multicellular spheroids of different sizes. We make one fit using only the smallest spheroid data and we are able to predict the SF for the larger spheroids. These predictions are acceptable particularly using bounded sensitivities. We conclude with the importance of taking into account the contribution of clonogenic hypoxic cells to radiosensitivity and with the convenience of using bounded local sensitivities to predict overall radiosensitivity parameters.
IJCNN'99. International Joint Conference on Neural Networks. Proceedings (Cat. No.99CH36339), 1999
We analyze the main characteristics of neural networks interacting between them and making a syst... more We analyze the main characteristics of neural networks interacting between them and making a system. The subnets are of Hopfield type. The synoptic intensities of the connections belonging to each of the sub-nets and those that connect both are established by Hebb's rule. We study the application and influence of an unlearning procedure that modifies the intensity of the synoptic
Polymer Engineering & Science, 1999
Unwersidad Nacional ak San Luis Ejercito de los Andes 950,5700 San Luis, Argentina
Journal of Theoretical Biology, 1980
Journal of Polymer Science Part B: Polymer Physics, 1994
Journal of Polymer Science Part B: Polymer Physics, 1990
The diffusion of gases through glassy polymers is studied and the effective diffusion coefficient... more The diffusion of gases through glassy polymers is studied and the effective diffusion coefficient D ' " is represented as the result of the superposition of two fundamental mechanisms, namely slipping and hopping. De" is calculated by a two-point correlation method. Comparisons are made with experimental data of Meares for diffusion coefficients of Kr, O,, He, and A in poly(viny1 acetate) in the glassy state. Good fits are obtained and yield significant parameters.
Journal of Polymer Science Part B: Polymer Physics, 1989
The diffusion of gases through partially crystalline polymers is studied. The effective diffusion... more The diffusion of gases through partially crystalline polymers is studied. The effective diffusion coefficient DeB is obtained as the result of the averaged superposition of two fundamental mechanisms, namely, diffusion through the crystallites is considered to be zero, and diffusion through the rubbery fraction of the polymer obeys a Fujita-like free-volume theory. The predicted Deff is compared with experimental data of Kreituss and Frisch. The behavior of the diffusion coefficient in terms of concentration and crystalline fraction is satisfactorily explained through the model.
Journal of Polymer Science Part B: Polymer Physics, 1996
In this work, a phenomenological model for the gas diffusion in partially crystalline polymers us... more In this work, a phenomenological model for the gas diffusion in partially crystalline polymers using differential effective medium theory is presented. By making an analogy with the power law known as Archie's law which relates the d.c. conductivity of a brine saturated porous rock to its porosity; we show that gas diffusion through semicrystalline polymers can be described in a similar way. It is assumed that the diffusion coefficient in the crystalline region is zero, while in the amorphous region it is given by a free volume model, and an effective diffusion coefficient Deff, is obtained using the mentioned analogy. The variation of Deff upon concentration is analyzed through its free volume dependence. The crystallinity dependence is considered through an average chain immobilization factor (p), which is explicitely derived. Finally, the results of this model are compared with experimental data given by Kreituss and Frisch, obtaining a good agreement. 0 1996 John Wiley & Sons, Inc. Keywords: diffusion through polymeric films Archie's law effective medium theory concentration dependence Geophysics, 4 3 , 1 2 5 0 (1978).
Journal of Polymer Science Part B: Polymer Physics, 1992
Glassy polymers are considered as inhomogeneous with regions in which the gas sorption follows He... more Glassy polymers are considered as inhomogeneous with regions in which the gas sorption follows Henry's law and others where it follows Langmuir's law. It is assumed that the linear dimensions of these regions are small compared with the macroscopic length of interest but large compared with the mean free path of the penetrant gas molecules. Applying an homogenization method it is shown that the average flux is directly proportional to the concentration gradient in the polymer. This relationship can be expressed in terms of an effective diffusion coefficient Deff, which depends on the details of the microstructure. D,ff is evaluated in the framework of the effective medium theory and compared with experimental data for diffusion of five vapors in ethylcellulose.
Journal of Physics A: Mathematical and General, 1998
We consider a fully connected Hopfield-like neural network as a set of N independent perceptrons.... more We consider a fully connected Hopfield-like neural network as a set of N independent perceptrons. We trained these perceptrons using the so-called inverse perceptron rule, obtaining a matrix of synaptic couplings, that make a number of spurious states unstable. We numerically determine the optimum number of spurious states, obtained by random shooting, that must be destabilized in order to obtain an improvement in performance. The unlearning procedure generated, is shown to be able to give a high-performance associative memory characterized by: (1) an enhancement in storaging capacity; (2) an enlargement in the size of attraction basins; (3) a reduction in the number of spurious attractors and (4) a reliable and fast retrieval.
Journal of Pharmaceutical Sciences, 1989
0 Sucrogel H-70, a recently synthesized polyester of sucrose, was investigated as a potenltial cl... more 0 Sucrogel H-70, a recently synthesized polyester of sucrose, was investigated as a potenltial clrug delivery matrix. In this study, the release of sodium salicylate was examined from a reservoir-controlled release device. It is shown that sodium salicylate release follows zero-order kinetics in the three media studied (i.e., water and simulated gastric and intestinal fluids).
Journal of Mathematical Analysis and Applications, 1982
Journal of Colloid and Interface Science, 1988
... 68, 2741 (1964). 5. Ponzi, M., Papa, J., Zgrablich, J., and Rivarola, JBP,AIChE J. 23, 347 (1... more ... 68, 2741 (1964). 5. Ponzi, M., Papa, J., Zgrablich, J., and Rivarola, JBP,AIChE J. 23, 347 (1977). 6. Horas, J., Marchese, J., and Rivarola, JBP, J. Chem. Phys. ... 13. Greg, SJ, and Sing, KSW, "Adsorption Surface Area and Porosity." Academic Press, London New York, 1967. 14. ...
J Phys a Math Gen, 1998
We consider a fully connected Hopfield-like neural network as a set of N independent perceptrons.... more We consider a fully connected Hopfield-like neural network as a set of N independent perceptrons. We trained these perceptrons using the so-called inverse perceptron rule, obtaining a matrix of synaptic couplings, that make a number of spurious states unstable. We numerically determine the optimum number of spurious states, obtained by random shooting, that must be destabilized in order to obtain an improvement in performance. The unlearning procedure generated, is shown to be able to give a high-performance associative memory characterized by: (1) an enhancement in storaging capacity; (2) an enlargement in the size of attraction basins; (3) a reduction in the number of spurious attractors and (4) a reliable and fast retrieval.
Se trata de responder bajo qué condiciones se cumple la convergencia a la distribución de Poisson... more Se trata de responder bajo qué condiciones se cumple la convergencia a la distribución de Poisson, para células tumorales sometidas a tratamientos radiobiológicos fraccionados, utilizando varias formas de administración de la dosis. Para ello también se comparan modelos que dan la probabilidad de control tumoral (TCP) usando datos experimentales obtenidos de la bibliografía. Se usan dos líneas celulares que crecen como megacolonias in vitro, las cuales son irradiadas con diversos esquemas de fraccionamiento: convencional y acelerado. Se concluye sobre las hipótesis fundamentales de los modelos utilizados y se obtiene información sobre los parámetros de cada modelo y la validez de los procesos que involucran. Se estudian, entre otros, la recuperación celular total o parcial, el efecto de la resensitización y de la repoblación celular producidos entre fracciones en ambos tipos de fraccionamiento. Se consideran los límites generalmente utilizados en mediciones de fracción de sobrevida y se analiza la validez de la aproximación de Poisson en cada caso.
Se considera la heterogeneidad de la población celular de un tumor cancerígeno. Tal heterogeneida... more Se considera la heterogeneidad de la población celular de un tumor cancerígeno. Tal heterogeneidad se manifiesta claramente en su respuesta a la radiación, produciendo que la radiocurabilidad esté determinada por las células más resistentes. Para evaluar la probabilidad de cura tumoral es determinante encontrar el correcto número de células clonogénicas, que también acusan heterogeneidad, la cual es modelada utilizando la estadística de Poisson con modelos de dos compartimientos. Se analiza también otro tipo de modelos para obtener la probabilidad de cura tumoral. En todos los casos el objetivo es determinar el correcto número de células clonogénicas, o sea, aquellas capaces de reproducir el tumor. También se considera el estado de oxigenación en el que se encuentran. Los resultados se comparan con datos experimentales de esferoides celulares de diversos tamaños. Estos sistemas in vitro son muy usados como sistema modelo en radioterapia. Palabras claves: probabilidad de control tumoral, células clonogénicas, hipoxia.
In this paper we compare different models for the tumor control probability (TCP ) using experime... more In this paper we compare different models for the tumor control probability (TCP ) using experimental data obtained from bibliography. Two cellular lines growing like megacolon ies in vitro are used and irradiated with different fractionation schemes: conventional and accelerated. We obtain conclusions on the fundamental hypothesis of each model and its usefulness for different types of division into fractions of the dosis. We obtain information about the parameters of each model and the validity of the involved processes. The following mechanisms are considered: total or partial cell recovery due to sub-lethal damages, the effect of resensitization and the cellular repopulation produced in fractions in both types of division into fractions.
Se utiliza un modelo de dos compartimientos para predecir la probabilidad de cura tumoral (TCP) e... more Se utiliza un modelo de dos compartimientos para predecir la probabilidad de cura tumoral (TCP) en esferoides celulares irradiados. Usando este modelo es posible determinar los parámetros de radiosensibil idad efectiva, considerando una distribución tipo mezcla gausiana para dichos parámetros. Con estos y aplicando la estadística de Poisson se obtiene una expresión para la probabilidad de cura tumoral. Se estudia el efecto de la radiación sobre las células en estado hipóxico (radioresistentes) y sobre aquellas en estado óxico (Menos radioresistentes). El análisis se cen tra en verificar que la curva de TCP es determinada por las células clonogénicas de mayor resistencia a la radiación. El modelo se aplica a esferoides celulares (MCTS) de distinto tamaño de una línea celular de adenocarcinoma de colon (Widr), obteniéndose interesantes correlaciones. La variación de la densidad de células clonogénicas y otros aspectos en el interior del esferoide son también considerados. A two-compar...
The delay time or time lag, i.e. the time to reach the stationary state, represents, all together... more The delay time or time lag, i.e. the time to reach the stationary state, represents, all together with the permeation, the dinamics of the diffusive process, and is of large use and usefulness to characterize the mass transport through polymeric films. Is important because is a measure of the difusive dinamics, and also because it depends on sorption equilibrium. We
Physics in Medicine and Biology, 2005
We model the heterogeneous response to radiation of multicellular tumour spheroids assuming posit... more We model the heterogeneous response to radiation of multicellular tumour spheroids assuming position- and volume-dependent radiosensitivity. We propose a method to calculate the overall radiosensitivity parameters to obtain the surviving fraction of tumours. A mathematical model of a spherical tumour with a hypoxic core and a viable rim which is a caricature of a real tumour is constructed. The model is embedded in a two-compartment linear-quadratic (LQ) model, assuming a mixed bivariated Gaussian distribution to attain the radiosensitivity parameters. Ergodicity, i.e., the equivalence between ensemble and volumetric averages is used to obtain the overall radiosensitivities for the two compartments. We obtain expressions for the overall radiosensitivity parameters resulting from the use of both a linear and a nonlinear dependence of the local radiosensitivity with position. The model's results are compared with experimental data of surviving fraction (SF) for multicellular spheroids of different sizes. We make one fit using only the smallest spheroid data and we are able to predict the SF for the larger spheroids. These predictions are acceptable particularly using bounded sensitivities. We conclude with the importance of taking into account the contribution of clonogenic hypoxic cells to radiosensitivity and with the convenience of using bounded local sensitivities to predict overall radiosensitivity parameters.
IJCNN'99. International Joint Conference on Neural Networks. Proceedings (Cat. No.99CH36339), 1999
We analyze the main characteristics of neural networks interacting between them and making a syst... more We analyze the main characteristics of neural networks interacting between them and making a system. The subnets are of Hopfield type. The synoptic intensities of the connections belonging to each of the sub-nets and those that connect both are established by Hebb's rule. We study the application and influence of an unlearning procedure that modifies the intensity of the synoptic
Polymer Engineering & Science, 1999
Unwersidad Nacional ak San Luis Ejercito de los Andes 950,5700 San Luis, Argentina
Journal of Theoretical Biology, 1980
Journal of Polymer Science Part B: Polymer Physics, 1994
Journal of Polymer Science Part B: Polymer Physics, 1990
The diffusion of gases through glassy polymers is studied and the effective diffusion coefficient... more The diffusion of gases through glassy polymers is studied and the effective diffusion coefficient D ' " is represented as the result of the superposition of two fundamental mechanisms, namely slipping and hopping. De" is calculated by a two-point correlation method. Comparisons are made with experimental data of Meares for diffusion coefficients of Kr, O,, He, and A in poly(viny1 acetate) in the glassy state. Good fits are obtained and yield significant parameters.
Journal of Polymer Science Part B: Polymer Physics, 1989
The diffusion of gases through partially crystalline polymers is studied. The effective diffusion... more The diffusion of gases through partially crystalline polymers is studied. The effective diffusion coefficient DeB is obtained as the result of the averaged superposition of two fundamental mechanisms, namely, diffusion through the crystallites is considered to be zero, and diffusion through the rubbery fraction of the polymer obeys a Fujita-like free-volume theory. The predicted Deff is compared with experimental data of Kreituss and Frisch. The behavior of the diffusion coefficient in terms of concentration and crystalline fraction is satisfactorily explained through the model.
Journal of Polymer Science Part B: Polymer Physics, 1996
In this work, a phenomenological model for the gas diffusion in partially crystalline polymers us... more In this work, a phenomenological model for the gas diffusion in partially crystalline polymers using differential effective medium theory is presented. By making an analogy with the power law known as Archie's law which relates the d.c. conductivity of a brine saturated porous rock to its porosity; we show that gas diffusion through semicrystalline polymers can be described in a similar way. It is assumed that the diffusion coefficient in the crystalline region is zero, while in the amorphous region it is given by a free volume model, and an effective diffusion coefficient Deff, is obtained using the mentioned analogy. The variation of Deff upon concentration is analyzed through its free volume dependence. The crystallinity dependence is considered through an average chain immobilization factor (p), which is explicitely derived. Finally, the results of this model are compared with experimental data given by Kreituss and Frisch, obtaining a good agreement. 0 1996 John Wiley & Sons, Inc. Keywords: diffusion through polymeric films Archie's law effective medium theory concentration dependence Geophysics, 4 3 , 1 2 5 0 (1978).
Journal of Polymer Science Part B: Polymer Physics, 1992
Glassy polymers are considered as inhomogeneous with regions in which the gas sorption follows He... more Glassy polymers are considered as inhomogeneous with regions in which the gas sorption follows Henry's law and others where it follows Langmuir's law. It is assumed that the linear dimensions of these regions are small compared with the macroscopic length of interest but large compared with the mean free path of the penetrant gas molecules. Applying an homogenization method it is shown that the average flux is directly proportional to the concentration gradient in the polymer. This relationship can be expressed in terms of an effective diffusion coefficient Deff, which depends on the details of the microstructure. D,ff is evaluated in the framework of the effective medium theory and compared with experimental data for diffusion of five vapors in ethylcellulose.
Journal of Physics A: Mathematical and General, 1998
We consider a fully connected Hopfield-like neural network as a set of N independent perceptrons.... more We consider a fully connected Hopfield-like neural network as a set of N independent perceptrons. We trained these perceptrons using the so-called inverse perceptron rule, obtaining a matrix of synaptic couplings, that make a number of spurious states unstable. We numerically determine the optimum number of spurious states, obtained by random shooting, that must be destabilized in order to obtain an improvement in performance. The unlearning procedure generated, is shown to be able to give a high-performance associative memory characterized by: (1) an enhancement in storaging capacity; (2) an enlargement in the size of attraction basins; (3) a reduction in the number of spurious attractors and (4) a reliable and fast retrieval.
Journal of Pharmaceutical Sciences, 1989
0 Sucrogel H-70, a recently synthesized polyester of sucrose, was investigated as a potenltial cl... more 0 Sucrogel H-70, a recently synthesized polyester of sucrose, was investigated as a potenltial clrug delivery matrix. In this study, the release of sodium salicylate was examined from a reservoir-controlled release device. It is shown that sodium salicylate release follows zero-order kinetics in the three media studied (i.e., water and simulated gastric and intestinal fluids).
Journal of Mathematical Analysis and Applications, 1982
Journal of Colloid and Interface Science, 1988
... 68, 2741 (1964). 5. Ponzi, M., Papa, J., Zgrablich, J., and Rivarola, JBP,AIChE J. 23, 347 (1... more ... 68, 2741 (1964). 5. Ponzi, M., Papa, J., Zgrablich, J., and Rivarola, JBP,AIChE J. 23, 347 (1977). 6. Horas, J., Marchese, J., and Rivarola, JBP, J. Chem. Phys. ... 13. Greg, SJ, and Sing, KSW, "Adsorption Surface Area and Porosity." Academic Press, London New York, 1967. 14. ...