R. Maceiras

Effect of Temperature on Rheological Properties of Different Jams

The rheological behavior of selected jams was analyzed at different temperatures, from 20 to 40°C in a rotational viscosimeter (HAAKE VT550). The rheograms were fitted with Power-Law, Carreau, Herschel-Bulkley, and Cross models. It was observed that the jams presented a pseudoplastic behavior, and the suspended solids influenced the consistency index.

Comparison of Rheological Behavior of Sweet and Salad Sauces

Abstract A comparative study of different commercial sauces was carried out from a rheological point of view. The different sauces were divided into sweet and salad, and for each sausage the behavior was studied at different temperatures. The power-law parameters, n and k, for sauces were calculated and their variation with the temperature was studied. On the other hand, the activation energy was calculated for the sweet sauces.

Aplicación de Nuevas Tecnologías en la Docencia Universitaria

Resumen Se presenta una aplicacion de las llamadas pildoras del conocimiento en el marco de las nuevas tecnologias en la docencia universitaria, desarrolladas en la Universidad de Vigo, Espana. Se analiza el concepto de pildora del conocimiento y se presenta una sobre el tema de equilibrio quimico de interes en Ingenieria Quimica y estudios afines. Las pildoras creadas tienen igual formato, y se basan en la definicion de Polimedia, tecnica muy valorada en desarrollos de nuevas tecnologias para la ensenanza ya que permite que el ponente interactue con la presentacion. El objetivo ultimo de las pildoras y en particular de la discutida en este trabajo es mejorar el proceso de aprendizaje del alumno y facilitar la integracion de las materias, todo esto en el marco del Espacio Europeo de Educacion Superior. Se analiza finalmente la cantidad de accesos de dichas pildoras en el tiempo y se concluye sobre las ventajas de su uso como tecnologia docente de apoyo a la ensenanza-aprendizaje. Palabras Clave: docencia universitaria, objeto de aprendizaje, pildora de conocimiento, ingenieria.

Experience of cooperative learning in engineering

The objective of this work is to share the authors’ experience towards a different mode of teaching/learning method. Cooperative learning (Jigsaw) was employed on the University of Vigos fourth-year engineering students. The results of the experience show that cooperative learning is quite a viable alternative to the classical way of lecturing at the university when the number of students is not too high. The authors’ observation indicates that students did not show a lot of interest towards the new learning style but their resistance changed once they began the activity. The Jigsaw method has proved to be a useful tool for improving the learning process so that students have the opportunity to participate actively in the learning activities.

Rheological Characterization of Commercial Baby Fruit Purees

The rheological behaviour of fruit purees was measured at different temperatures (20°C–40°C) in a rotational viscometer. The rheograms were fitted with the Power Law or Ostwald de Waele model, the Herschel-Bulkley model, the Casson model, and the Cross model. The best adjustment was obtained with the Cross model, except for systems fruit purees 2 and 4, which were fitted satisfactorily with Power Law model. Flow curves exhibited at all temperatures a pseudoplastic character after applying a shear stress higher than a critical value.

Rheological Behavior of Powdered Baby Foods

The rheological properties of four types of powdered baby foods have been investigated. Density and apparent viscosity have been measured at different temperatures. The values of the both properties decrease with the temperature. The experimental data belonging to apparent viscosity are represented by a power law. The relationship between the power law parameters and temperature has been analyzed.

Comparison of Rheological Behaviour of Salad Sauces

Seventeen commercial salad sauces, made by different manufacturers, were studied to examine their rheological properties. Rheological studies include determination of the following: (a) flow curves with a controlled shear rate or shear stress, and (b) curves showing the time and temperature dependence of apparent viscosity. Apparent viscosity was correlated using the power-law model. The flow behaviour index, n, and the consistency index, K, were calculated and their variation with the temperature (between 20 and 40°C) was studied. Their values varied between 0.19 and 0.51, for n, and between 2.39 and 60.5, for K.

Adaptation of a virtual campus for mobile learning devices

Currently, almost all Spanish Universities offer their students access to a virtual campus consisting essentially of one or more e-learning platforms, which contain the educational material of most of the subjects taught at the university. Although the aim of these e-learning platforms is the learning in virtual format, mainly they are used by the teachers to supplement the lectures (b-learning). Due to the nature and design of such platforms and learning materials, access to the contents is restricted to the use of personal computers (desktops or laptops with screens large enough). This paper describes the actions in terms of necessaries modification of software to allow access to the contents stored in the virtual campus through various types of mobile devices.

Rheological Properties of Cooking Creams: Effect of Freeze-Thaw Treatment

Rheological characteristics of commercial creams were investigated at different freeze-thaw conditions. This study was carried out to determine the effect of the freeze-thaw treatment on rheological behaviour and the activation energy in different commercial creams. Freeze-thaw treatment was made at different times of frozen storage within a range from 0 to 6 weeks. For each freezing cycle, the sample was submitted to rheological measurements within range of temperature between 20 and 40° C. A rotational, concentric cylinder viscosimeter Viscotester VT550 (Germany) type Searle was used in this work. The apparent viscosity is defined as the ratio of shear stress and shear rate, which was varied between 17.8 and 445 s-1. The Power Law or Oswaltd Waele model describes well the rheological behaviour of the analyzed samples. Furthermore, in all cases sample viscosity increased when was exposed to freeze-thaw treatment with respect to the not treated sample. And other hand, the activation energy has high values; hence there is clear evidence that the rheological behaviour presents a high dependence with the temperature.

A Study on Techniques for Microalgae Separation and Lipid Extraction for Desmodesmus subspicatus

An alternative for production of biodiesel is the use of lipids from microalgae. The process has different steps such as microalgae cultivation harvesting, lipids extraction, and transesterification. One of the most important steps is the microalgae separation from the culture before lipid extraction. Thus, the purpose of the present study is to compare different methods of microalgae harvesting and total lipids extracting for freshwater Desmodesmus subspicatus microalga. The methods used for harvesting were chemical coagulation and electrocoagulation. Both methods achieved high values of recovery efficiency (90%). However, electrocoagulation was considered more attractive because of its lower power consumption and the requirement of high dosages of coagulants for chemical coagulation. Two methods of extraction, Soxhlet and ultrasound irradiation, were tested using different solvents. The highest lipid extraction (36%) was obtained with ultrasound irradiation and ethanol. Thus, ultrasound-assisted extraction appears to be an efficient method for lipid extraction from D. subspicatus.