Cristian Ioan - Academia.edu (original) (raw)

Papers by Cristian Ioan

Journal of Theoretical Biology, 2010

After eating a liquid or a semi-liquid food product, a thin film responsible for the dynamic prof... more After eating a liquid or a semi-liquid food product, a thin film responsible for the dynamic profile of aroma release coats the pharyngeal mucosa. The aim of this article was to analyse the fluid mechanics of pharyngeal peristalsis and to develop a simple biomechanical model in order to understand the role of saliva and food bolus viscosity on the coating of pharyngeal mucosa. We began by analysing the physiology and the biomechanics of swallowing in order to determine relevant model assumptions. This analysis of the literature clarified the types of mechanical solicitations applied on the food bolus. Moreover, we showed that the pharyngeal peristalsis in the most occluded region is equivalent to a forward roll coating process, the originality of which is lubrication by a film of saliva. A model based on the lubrication theory for Newtonian liquids was developed in dimensionless form. The parametric study showed the strong influence of relative saliva thickness on the food bolus coating. A specific experimental device was designed that confirms the model predictions. Two sets of conditions that depend on the relative thickness of saliva were distinguished. The first is characterised by a relatively thin film of saliva: food bolus viscosity has a strong impact on mucosa coating. These phenomena are well represented by the model developed here. The second is obtained when the saliva film is relatively thick: hydrodynamic mixing with saliva, interdiffusion or instabilities may govern mucosa coating. Finally, these results were extrapolated to determine the influence of food bolus viscosity on the dynamic profile of flavour release according to physiological parameters.

Journal of Food Engineering, 2008

The present study deals with the respiratory activity of the microbial consortia established on s... more The present study deals with the respiratory activity of the microbial consortia established on surface-mould cheese. A software sensor was developed, from a model linking the operating conditions established in the ripening room (temperature, relative humidity, carbon dioxide and oxygen concentration) to the cheese mass dynamic. It estimated the respiratory activity of the microbial consortia based on mass measurement only, without atmospheric gas composition sensors or off-line measurements. After some simplifications of the model, this observer can be seen as an integral Luenberger observer, with analytically defined gain values. This approach was validated on two ripening trials. Relative errors between estimated and calculated (from carbon dioxide and oxygen concentration measurements) respiratory activity were equal to 3.02% and 8.83% for Run 1 and Run 2, respectively.

Journal of The American Ceramic Society, 2007

Resistive oxygen sensors based on gallium oxide were fabricated in order to analyze their sensing... more Resistive oxygen sensors based on gallium oxide were fabricated in order to analyze their sensing performances (as sensitivity, response, and recovery time) in an oxygen atmosphere at 1000°C. We prepared three types of sensors using a β-Ga2O3 single crystal in a sandwich structure with Pt pad electrodes and β-Ga2O3 polycrystalline thin films deposited by using both the sputtering technique and the chemical solution deposition method. For thin-film sensors, Pt interdigital electrodes were deposited on the surface of the films using the lift-off method. X-ray diffraction and atomic force microscopy investigations were performed to compare the structure and surface morphology of the samples. We achieved a response time of 10 s at 1000°C, while the sensitivity was 1.03 for the single crystal and 1.35–1.45 for thin films. The sensing properties depend on the preparation condition of Ga2O3 devices.

Food Chemistry

The aim of this study was to investigate the influence of the water activity on the stability of ... more The aim of this study was to investigate the influence of the water activity on the stability of lyophilised lactic acid bacteria, especially in the solid glassy region. Lactobacillus bulgaricus CFL1 was co-lyophilised with sucrose and stored under controlled relative humidity at 25°C. Glass transition temperature (T g ), water activity, water content and loss of specific acidification activity during storage were determined. The rates of bacteria degradation were analysed as a function of water activity and as a function of the temperature difference between storage temperature and T g . Above T g , the degradation rate appeared related to the physical changes of the amorphous matrix. Below T g , the optimal stability of the lyophilised bacteria was observed in the intermediate water activity range 0.1-0.214. An integrated analysis of the relationships between water activity, T g , water content and biological activity appeared as a promising approach for optimising the freeze-drying process and predicting the storage stability.

Biological Conservation, 2010

In this paper we give a generalization of some results due to T. Takahashi [5] and M. Okumura [4]... more In this paper we give a generalization of some results due to T. Takahashi [5] and M. Okumura [4]. Explicitly, we study an equation of the form R(X,Y)A=0 where X,Y are arbitrary vector fields on a Sasakian manifold and A a (1,3)-tensor field which generalizes the Riemann curvature tensor, Weyl conformal curvature tensor, Weyl projective curvature tensor and Yano concircular curvature tensor. The result which we obtain says that in complementary conditions the manifold is of constant curvature.

Journal of Theoretical Biology, 2010

After eating a liquid or a semi-liquid food product, a thin film responsible for the dynamic prof... more After eating a liquid or a semi-liquid food product, a thin film responsible for the dynamic profile of aroma release coats the pharyngeal mucosa. The aim of this article was to analyse the fluid mechanics of pharyngeal peristalsis and to develop a simple biomechanical model in order to understand the role of saliva and food bolus viscosity on the coating of pharyngeal mucosa. We began by analysing the physiology and the biomechanics of swallowing in order to determine relevant model assumptions. This analysis of the literature clarified the types of mechanical solicitations applied on the food bolus. Moreover, we showed that the pharyngeal peristalsis in the most occluded region is equivalent to a forward roll coating process, the originality of which is lubrication by a film of saliva. A model based on the lubrication theory for Newtonian liquids was developed in dimensionless form. The parametric study showed the strong influence of relative saliva thickness on the food bolus coating. A specific experimental device was designed that confirms the model predictions. Two sets of conditions that depend on the relative thickness of saliva were distinguished. The first is characterised by a relatively thin film of saliva: food bolus viscosity has a strong impact on mucosa coating. These phenomena are well represented by the model developed here. The second is obtained when the saliva film is relatively thick: hydrodynamic mixing with saliva, interdiffusion or instabilities may govern mucosa coating. Finally, these results were extrapolated to determine the influence of food bolus viscosity on the dynamic profile of flavour release according to physiological parameters.

Journal of Food Engineering, 2008

The present study deals with the respiratory activity of the microbial consortia established on s... more The present study deals with the respiratory activity of the microbial consortia established on surface-mould cheese. A software sensor was developed, from a model linking the operating conditions established in the ripening room (temperature, relative humidity, carbon dioxide and oxygen concentration) to the cheese mass dynamic. It estimated the respiratory activity of the microbial consortia based on mass measurement only, without atmospheric gas composition sensors or off-line measurements. After some simplifications of the model, this observer can be seen as an integral Luenberger observer, with analytically defined gain values. This approach was validated on two ripening trials. Relative errors between estimated and calculated (from carbon dioxide and oxygen concentration measurements) respiratory activity were equal to 3.02% and 8.83% for Run 1 and Run 2, respectively.

Journal of The American Ceramic Society, 2007

Resistive oxygen sensors based on gallium oxide were fabricated in order to analyze their sensing... more Resistive oxygen sensors based on gallium oxide were fabricated in order to analyze their sensing performances (as sensitivity, response, and recovery time) in an oxygen atmosphere at 1000°C. We prepared three types of sensors using a β-Ga2O3 single crystal in a sandwich structure with Pt pad electrodes and β-Ga2O3 polycrystalline thin films deposited by using both the sputtering technique and the chemical solution deposition method. For thin-film sensors, Pt interdigital electrodes were deposited on the surface of the films using the lift-off method. X-ray diffraction and atomic force microscopy investigations were performed to compare the structure and surface morphology of the samples. We achieved a response time of 10 s at 1000°C, while the sensitivity was 1.03 for the single crystal and 1.35–1.45 for thin films. The sensing properties depend on the preparation condition of Ga2O3 devices.

Food Chemistry

The aim of this study was to investigate the influence of the water activity on the stability of ... more The aim of this study was to investigate the influence of the water activity on the stability of lyophilised lactic acid bacteria, especially in the solid glassy region. Lactobacillus bulgaricus CFL1 was co-lyophilised with sucrose and stored under controlled relative humidity at 25°C. Glass transition temperature (T g ), water activity, water content and loss of specific acidification activity during storage were determined. The rates of bacteria degradation were analysed as a function of water activity and as a function of the temperature difference between storage temperature and T g . Above T g , the degradation rate appeared related to the physical changes of the amorphous matrix. Below T g , the optimal stability of the lyophilised bacteria was observed in the intermediate water activity range 0.1-0.214. An integrated analysis of the relationships between water activity, T g , water content and biological activity appeared as a promising approach for optimising the freeze-drying process and predicting the storage stability.

Biological Conservation, 2010

In this paper we give a generalization of some results due to T. Takahashi [5] and M. Okumura [4]... more In this paper we give a generalization of some results due to T. Takahashi [5] and M. Okumura [4]. Explicitly, we study an equation of the form R(X,Y)A=0 where X,Y are arbitrary vector fields on a Sasakian manifold and A a (1,3)-tensor field which generalizes the Riemann curvature tensor, Weyl conformal curvature tensor, Weyl projective curvature tensor and Yano concircular curvature tensor. The result which we obtain says that in complementary conditions the manifold is of constant curvature.