Transient shear flow of model lithium lubricating greases

This paper deals with the analysis of the transient shear flow behavior of lithium lubricating greases differing in soap concentration and base oil viscosity. The shear-induced evolution of grease microstructure has been studied by means of stress-growth experiments. With this aim, different lubricating grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and the viscosity of the base oil, according to a RSM statistical design. Moreover, atomic force microscopy (AFM) observations were carried out. The transient stress response can be successfully described by the generalized Leider-Bird model based on two exponential terms. Different rheological parameters, related to both the elastic response and the structural breakdown of greases, have been analysed. In this sense, it has been found that the elastic properties of lithium lubricating greases were highly influenced by soap concentration and oil viscosity. The stress overshoot, τ _max, depends linearly on both variables in the whole shear rate range studied, although the effect of base oil viscosity on this parameter is opposite at low and high shear rates. Special attention has been given to the first part of the stress-growth curve. In this sense, it can be deduced that the “yielding” energy density not only depends on grease composition, but also on shear rate. Moreover, an interesting asymptotic tendency has been found for both the “yielding” energy density and the stress overshoot by increasing shear rate. The asymptotic values of these parameters have been correlated to the friction coefficient obtained in a ball-disc tribometer.     

Recycled and virgin LDPE as rheology modifiers of lithium lubricating greases: A comparative study

In this work, a new application for recycled low‐density polyethylene (LDPE), as rheology modifier of standard lithium lubricating grease formulations, was studied. The effectiveness of this additive was compared with that achieved with a virgin LDPE. With this aim, both types of polymers were added to the formulation during the manufacturing process of greases, following the same standard protocol, to reinforce the role of the thickening agent, the lithium 12‐hidroxystearate. The effect that both lithium soap and LDPE concentrations exert on the rheology of lubricating grease formulations and its relationship with grease microstructure were discussed. Lubricating greases were rheologically characterized through small‐amplitude oscillatory shear and viscous flow measurements. In addition to these, scanning electron microscopy observations and mechanical stability tests were also carried out. In all cases, an increase in soap concentration yields higher values of apparent viscosity and linear viscoelasticity functions. On the other hand, the values of the rheological functions obtained for recycled LDPE‐based lubricating greases are, in general, higher than those obtained for virgin LDPE‐based grease formulations. However, the structural skeleton developed in greases containing recycled LDPE demonstrates less resistance to severe working conditions, showing lower mechanical stability than virgin LDPE‐based grease formulations. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Analysis of volatile compounds in some typical Brazilian fruits and juices by SPME-GC method

This paper describes the analysis of volatile organic compounds (VOC) in typical Brazilian fruit and fruit juices by a solid-phase microextraction (SPME) method using a capillary gas chromatography system with flame ionization detection and mass spectrometry (GC-MS). A SPME holder with a 100-µm polydimethilsiloxane fibre coating was utilized. The optimal conditions were desorption at 220°C for 1 min, absorption at 50°C for 20 min and 4.00 ml of sample in the headspace vial. The method gave good precision and showed a linear response. More than 100 VOC were identified in the fruit and juices studied by GC-MS. The method was employed to quantify ethanol, naphthalene and benzoic acid in four different species of Brazilian fruit and their juices.     

Case-Based Reasoning and System Identification for Control Engineering Learning

This paper presents a novel Web service encouraging active learning by students. The students are able to use physical systems in a remote way, obtaining explanatory feedback on whether their actions are correct or incorrect. This service is based on system identification (SI) techniques to gain a knowledge of the physical system involved and case-based reasoning (CBR) for exploiting this knowledge. Uniting CBR and SI, an emulation of the real physical system is achieved that permits resolution of the problems of real-time access and simultaneous multiuser access that currently exist in remote-learning laboratories.     

Preparation of ITQ-29 (Al-free zeolite A) membranes

Membranes consisting of Al-free ITQ-29 (a zeolite with the LTA-type structure) have been prepared on alumina tubular supports by seeded liquid phase hydrothermal synthesis. A supramolecular organic structure-directing agent (SDA) was used for the synthesis of ITQ-29 that must be removed from the zeolite pores to activate the membrane for permeation. The high temperature needed to decompose SDA from small-pore zeolites could create thermal stresses that affect the final membrane quality. Because of this, the effect of the atmosphere (N₂, O₂, air and O₃/air) and temperature of the membrane calcination process has been studied. An ITQ-29 membrane activated by means of the combination of pyrolytic (at 723 K) and ozonization (at 473–573 K) treatments gave the best results, with N₂/CH₄ and N₂/propane selectivities well above the corresponding Knudsen values.     

Biohydrogenation intermediates are differentially deposited between polar and neutral intramuscular lipids of lambs

The deposition of C₁₈ fatty acids (FA), especially in rumen biohydrogenation intermediates, was studied using 36 lambs fed four diets with graded proportions of sunflower oil (SO) and linseed oil (LO). Lambs were fed one of four diets consisting on dehydrated lucerne with either: 6% SO, 4% SO plus 2% LO, 2% SO plus 4% LO and 6% LO. The profile of C₁₈ FA was greatly affected by replacement of SO with LO in both lipid fractions. In PL, oil replacement led to an extensive substitution of 18:2n‐6 with 18:3n‐3 and cis‐9 18:1, resulting in a fairly constant degree of unsaturation of C₁₈ FA in membrane PL. C₁₈ FA were differentially incorporated in NL and PL. Cis‐isomers like cis‐11; cis‐12; cis‐15 18:1 and cis‐12, cis‐15 18:2 were preferentially incorporated in PL with the exception of cis‐9, cis‐15 18:2. Trans C₁₈ FA, including CLA isomers, were preferentially incorporated in NL with the exception of cis‐11, trans‐13 18:2. The preferential deposition of biohydrogenation derived trans C₁₈ FA, including CLA isomers in NL, suggests that their potential to change membrane FA composition and structure is low.     

Providing universally accessible interactive services through TV sets: implementation and validation with elderly users

One of the challenges that Ambient Intelligence (AmI) faces is the provision of a usable interaction concept to its users, especially for those with a weak technical background. In this paper, we describe a new approach to integrate interactive services provided by an AmI environment with the television set, which is one of the most widely used interaction client in the home environment. The approach supports the integration of different TV set configurations, guaranteeing the possibility to develop universally accessible solutions. An implementation of this approach has been carried out as a multimodal/multi-purpose natural human computer interface for elderly people, by creating adapted graphical user interfaces and navigation menus together with multimodal interaction (simplified TV remote control and voice interaction). In addition, this user interface can also be suited to other user groups. We have tested a prototype that adapts the videoconference and the information service with a group of 83 users. The results from the user tests show that the group found the prototype to be both satisfactory and efficient to use.