On the yield stress of complex materials

F. Calderas,E. E. Herrera-Valencia,A. Sanchez-Solis,O. Manero,L. Medina-Torres,A. Renteria,G. Sanchez-Olivares 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.4

In the present work, the yield stress of complex materials is analyzed and modeled using the Bautista-Manero-Puig (BMP) constitutive equation, consisting of the upper-convected Maxwell equation coupled to a kinetic equation to account for the breakdown and reformation of the fluid structure. BMP model predictions for a complex fluid in different flow situations are analyzed and compared with yield stress predictions of other rheological models, and with experiments on fluids that exhibit yield stresses. It is shown that one of the main features of the BMP model is that it predicts a real yield stress (elastic solid or Hookean behavior) as one of the material parameters, the zero shear-rate fluidity, is zero. In addition, the transition to fluid-like behavior is continuous, as opposed to predictions of more empirical models.

Rheological behavior of blood in Wistar rats with different total cholesterol levels

Medina-Torres Luis,Calderas Fausto,Calderas Fausto,Núñez–Ramírez Diola-Marina,Castro Andrés Navarrete,Bernad-Bernad Ma. Josefa,Manero Octavio 한국유변학회 2022 Korea-Australia rheology journal Vol.34 No.4

Blood is a rheologically complex suspension, in which the soluble fraction contains proteins, total cholesterol and triglycerides. The blood rheological behavior is strongly affected by the concentration of these components. This work evaluates the total cholesterol effect on the rheological behavior of Wistar rat blood by means of an in vitro study. Twenty-one rats were divided into 3 groups, each one had an assigned diet with different fat content: reference group (RG) with 3%, medium fat content group (MG) with 4.5% and high-fat content group (HG) with 6.5%; in the latter group, mixed-vegetable fat was added. From each group, intraocular representative blood samples were taken with time lapse of 15 days between each sampling followed by biochemical and hemo-rheological tests. The first analysis detected changes in total cholesterol levels, attributed to the rat metabolism, formation of adipose tissue and competition for food. The second test consisted in steady simple-shear and linear oscillatory flow. The linear viscoelastic spectra reveal that the viscous modulus is larger than the elastic modulus (G > G′), with simple-shear viscosity exhibiting shear-thinning behavior. An important finding is a pseudo-solid- like behavior at low frequencies (1 rad/s) akin to the presence of yield stresses in the high-fat content group after 30 days, revealing strong interactions between total cholesterol levels and blood cells. The hemo-rheological tests represent a promising alternative to identify pathologies present in the blood (total cholesterol, digestive problems, and diabetes).

Effect of cholesterol and triglycerides levels on the rheological behavior of human blood

Leonardo Moreno,Fausto Calderas,Guadalupe Sanchez-Olivares,Luis Medina-Torres,Antonio Sanchez-Solis,Octavio Manero 한국유변학회 2015 Korea-Australia rheology journal Vol.27 No.1

Important public health problems worldwide such as obesity, diabetes, hyperlipidemia and coronary diseases are quite common. These problems arise from numerous factors, such as hyper-caloric diets, sedentary habits and other epigenetic factors. With respect to Mexico, the population reference values of total cholesterol in plasma are around 200 mg/dL. However, a large proportion has higher levels than this reference value. In this work, we analyze the rheological properties of human blood obtained from 20 donors, as a function of cholesterol and triglyceride levels, upon a protocol previously approved by the health authorities. Samples with high and low cholesterol and triglyceride levels were selected and analyzed by simple-continuous and linear-oscillatory shear flow. Rheometric properties were measured and related to the structure and composition of human blood. In addition, rheometric data were modeled by using several constitutive equations: Bautista-Manero-Puig (BMP) and the multimodal Maxwell equations to predict the flow behavior of human blood. Finally, a comparison was made among various models, namely, the BMP, Carreau and Quemada equations for simple shear rate flow. An important relationship was found between cholesterol, triglycerides and the structure of human blood. Results show that blood with high cholesterol levels (400 mg/dL) has flow properties fully different (higher viscosity and a more pseudo-plastic behavior) than blood with lower levels of cholesterol (tendency to Newtonian behavior or viscosity plateau at low shear rates)

Rheology and gel point of the enzymatic hydrolysis of urea in the presence of urease

R. Serrato-Millán,L. Medina-Torres,F. Calderas,B.L. España-Sánchez,M. Estevez,A.R. Hernandez-Martínez,M. Cruz-Soto,I.C. Sánchez,R. Gómez-García,I. Sánchez-Betancourt,M.C. Velasquillo-Martínez,G. Luna- 한국유변학회 2017 Korea-Australia rheology journal Vol.29 No.1

This study reports on the rheology of the gelation kinetics of raw chitosan (CTS) solutions (2% w/v) produced by enzymatic hydrolysis of urea at different urea concentrations (40, 50, 60, 80, and 100 mM) in the presence of urease at 1 U/mL. Viscoelastic parameters and pH values were evaluated during gelation process and the rheological properties of CTS hydrogels produced were monitored after 24 h at 37°C to simulate human body temperatures. pH measurements suggest that above some critical urea concentration (50 mM) the time required (tgel) to reach the critical pH gelation shows no dependence on urea concentration (tgel was ca. 70 minutes). Above 50 mM of urea concentration, CTS hydrogels exhibit an elastic modulus G' higher than the viscous modulus G'' with no frequency dependence characteristic of a gel behavior. Gelation kinetics analyzed by rheology suggest that the G' (i.e., structure) development depends on urea concentration during solution neutralization.

Study of the Rheological Properties of a Fermentation Broth of the Fungus Beauveria bassiana in a Bioreactor Under Different Hydrodynamic Conditions

Nunez-Ramirez, Diola Marina,Medina-Torres, Luis,Valencia-Lopez, Jose Javier,Calderas, Fausto,Lopez-Miranda, Javier,Medrano-Roldan, Hiram,Solis-Soto, Aquiles The Korean Society for Microbiology and Biotechnol 2012 Journal of microbiology and biotechnology Vol.22 No.11

Fermentation with filamentous fungi in a bioreactor is a complex dynamic process that is affected by flow conditions and the evolution of the rheological properties of the medium. These properties are mainly affected by the biomass concentration and the morphology of the fungus. In this work, the rheological properties of a fermentation with the fungus Beauveria bassiana under different hydrodynamic conditions were studied and the rheological behavior of this broth was simulated through a mixture of carboxymethyl cellulose sodium and cellulose fibers (CMCNa-SF). The bioreactor was a 10 L CSTR tank operated at different stir velocities. Rheological results were similar at 100 and 300 rpm for both systems. However, there was a significant increase in the viscosity accompanied by a change in the consistence index, calculated according to the power law model, for both systems at 800 rpm. The systems exhibited shear-thinning behavior at all stir velocities, which was determined with the power law model. The mixing time was observed to increase as the cellulose content in the system increased and, consequently, the efficiency of mixing diminished. These results are thought to be due to the rheological and morphological similarities of the two fungal systems. These results will help in the optimization of scale-up production of these fungi.

Simultaneous pulsatile flow and oscillating wall of a non-Newtonian liquid

E.E. Herrera-Valencia,M.L. Sánchez-Villavicencio,F. Calderas,M. Pérez-Camacho,L. Medina-Torres 한국유변학회 2016 Korea-Australia rheology journal Vol.28 No.4

In this work, analytical predictions of the rectilinear flow of a non-Newtonian liquid are given. The fluid is subjected to a combined flow: A pulsatile time-dependent pressure gradient and a random longitudinal vibration at the wall acting simultaneously. The fluctuating component of the combined pressure gradient and oscillating flow is assumed to be of small amplitude and can be adequately represented by a weakly stochastic process, for which a quasi-static perturbation solution scheme is suggested, in terms of a small parameter. This flow is analyzed with the Tanner constitutive equation model with the viscosity function represented by the Ellis model. According to the coupled Tanner-Ellis model, the flow enhancement can be separated in two contributions (pulsatile and oscillating mechanisms) and the power requirement is always positive and can be interpreted as the sum of a pulsatile, oscillating, and the coupled systems respectively. Both expressions depend on the amplitude of the oscillations, the perturbation parameter, the exponent of the Ellis model (associated to the shear thinning or thickening mechanisms), and the Reynolds and Deborah numbers. At small wall stress values, the flow enhancement is dominated by the axial wall oscillations whereas at high wall stress values, the system is governed by the pulsating noise perturbation. The flow transition is obtained for a critical shear stress which is a function of the Reynolds number, dimensionless frequency and the ratio of the two amplitudes associated with the pulsating and oscillating perturbations. In addition, the flow enhancement is compared with analytical and numerical predictions of the Reiner-Phillipoff and Carreau models. Finally, the flow enhancement and power requirement are predicted using biological rheometric data of blood with low cholesterol content.

Fused roots of maxillary molars: characterization and prevalence in a Latin American sub-population: a cone beam computed tomography study

Marcano-Caldera, Maytte,Mejia-Cardona, Jose Luis,Blanco-Uribe, Maria del Pilar,Chaverra-Mesa, Elena Carolina,Rodriguez-Lezama, Didier,Parra-Sanchez, Jose Hernan The Korean Academy of Conservative Dentistry 2019 Restorative Dentistry & Endodontics Vol.44 No.2

Objectives: The upper molars generally have three roots; therefore, different combinations of fusion can occur, increasing the possibility of finding more complex root canal systems. The purpose of this study was to evaluate the prevalence and characterization of fused roots in first and second maxillary molars using cone-beam computed tomography (CBCT) in a Colombian population. Materials and Methods: A total of 1274 teeth were evaluated, of which 534 were maxillary first molars and 740 were maxillary second molars. Axial sections were made at the cervical, middle, and apical levels to determine the prevalence of root fusion and the types of fusion. Results: Overall, 43% of the molars (n = 551) presented some type of fused root. Root fusion was present in 23.4% of the maxillary first molars. The most frequent type of fused root was type 3 (distobuccal-palatal; DB-P) (58.9%). Root fusion was observed in 57.6% of the maxillary second molars, and the most prevalent type of fused root was type 6 (cone-shaped) (45.2%). Of the maxillary molars, 12.5% were classified as C-shaped. Conclusion: Within the limitations of this study, there was a high prevalence of fused roots in maxillary molars in the Colombian population, mainly in the maxillary second molars. In first molars, the most common type of fused root was type 3 (DB-P) and in second molars, the most common type was type 6 (cone-shaped). Additionally, molars with root fusion presented variation at different levels of the radicular portion, with implications for treatment quality.

Removal of textile dyes in wastewater using polyelectrolytes containing tetrazole groups

Martín Caldera-Vil,Alejandra-Alicia Peláez-Cid,Miriam-Amelia Martins-Alho,Ana-María Herrera-González 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.12

Textile dyes are some of the pollutants which have received the most attention because of the large volume of wastewater generated by the textile industry. Removal by means of adsorption is one of the most versatile alternatives to treat these effluents. Even though different adsorbents such as activated carbons and mineral materials have been proposed, polymeric adsorbents are a viable alternative. This work reports for the first time the use of polyelectrolyte PTZ and macroelectrolyte MTZ containing tetrazole groups as adsorbents useful in the textile dyes removal present in aqueous solutions and wastewater. Because of the anionic character of the tetrazole group, MTZ exhibits selective adsorption capabilities for cationic dyes of up to 156.25mg·g1. The kinetic study of the process of adsorption shows that PTZ and MTZ fit a pseudo second-order model. MTZ also shows utility as a flocculant agent in the treatment of wastewater containing dyes Indigo Blue and Reactive Black. The results showed that PTZ and MTZ may be used in the treatment of wastewater in a process of coagulation-flocculation followed by the treatment by adsorption. This twostage treatment removed up to 95% of the dye present in the wastewater. As well as removing the dyes, the values for COD, suspended solids, pH, and color of the wastewater decreased, thus significantly improving its quality.

Fused roots of maxillary molars: characterization and prevalence in a Latin American sub-population: a cone beam computed tomography study

Maytté Marcano-Caldera,Jose Luis Mejia-Cardona,María del Pilar Blanco-Uribe,Elena Carolina Chaverra-Mesa,Didier Rodríguez-Lezama,Jose Hernán Parra-Sánchez 대한치과보존학회 2019 Restorative Dentistry & Endodontics Vol.44 No.2

Objectives: The upper molars generally have three roots; therefore, different combinations of fusion can occur, increasing the possibility of finding more complex root canal systems. The purpose of this study was to evaluate the prevalence and characterization of fused roots in first and second maxillary molars using cone-beam computed tomography (CBCT) in a Colombian population. Materials and Methods: A total of 1274 teeth were evaluated, of which 534 were maxillary first molars and 740 were maxillary second molars. Axial sections were made at the cervical, middle, and apical levels to determine the prevalence of root fusion and the types of fusion. Results: Overall, 43% of the molars (n = 551) presented some type of fused root. Root fusion was present in 23.4% of the maxillary first molars. The most frequent type of fused root was type 3 (distobuccal-palatal; DB-P) (58.9%). Root fusion was observed in 57.6% of the maxillary second molars, and the most prevalent type of fused root was type 6 (cone-shaped) (45.2%). Of the maxillary molars, 12.5% were classified as C-shaped. Conclusion: Within the limitations of this study, there was a high prevalence of fused roots in maxillary molars in the Colombian population, mainly in the maxillary second molars. In first molars, the most common type of fused root was type 3 (DB-P) and in second molars, the most common type was type 6 (cone-shaped). Additionally, molars with root fusion presented variation at different levels of the radicular portion, with implications for treatment quality.

The severity of earthquake events – statistical analysis and classification

Mohammad Ansari Esfeh,H. Jithamala Caldera,Seiran Heshami,Nadia Moshahedi,Sumedha Chandana Wirasinghe 서울시립대학교 도시과학연구원 2016 도시과학국제저널 Vol.20 No.2

Earthquake events are natural disasters that can pose a threat to people’s safety as well as their homes and possessions. In this paper, the severity level of earthquake disasters is addressed using the US National Oceanic and Atmospheric Administration (NOAA) database. A total of 5841 earthquake incidents are recorded that happened between 2150 BCE and 2015 CE. Few studies have done a comprehensive statistical analysis of the consequences of earthquakes. To address this gap, and after determining the probability distribution function of the number of fatalities, we evaluate the distribution of earthquakes with extreme fatalities to determine the severity levels according to the fatality-based disaster scale introduced by Wirasinghe, Caldera, Durage, and Ruwanpura [(2013). Preliminary analysis and classification of natural disasters. Proceedings of the ninth annual conference of the International Institute for Infrastructure, Renewal and Reconstruction (IIIRR), Queensland University of Technology, Brisbane, Australia, July 2013, Section B1.2, p. 11]. To this end, three different methods of determining the extreme events are considered: peak over threshold, Rth order, and eventbased and location-based block maxima. Moreover, a comprehensive collinearity analysis is performed to investigate any correlation and linear dependency between the earthquake parameters (magnitude, intensity, and focal depth) and the consequences in terms of earthquake fatalities. The severity classification based on block maxima has more detailed severity classes; hence, it is superior to the other two methods. For block maxima, the probability of a lower level disaster (Emergency to Catastrophe Type 1) being the extreme disaster is higher for the location (country)-based data set compared to the event-based worldwide data set, while the probability of a higher level disaster (Catastrophe Type 2 and above) being the extreme disaster is lower. These probabilities are to be expected because a single country, even over the full time period, is less likely to have a massive disaster compared to the world when a large number of extreme events, in this case 100, are considered.