oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2019 ( 125 )

2018 ( 817 )

2017 ( 834 )

2016 ( 1134 )

Custom range...

Search Results: 1 - 10 of 491344 matches for " M.F.;Abreu "
All listed articles are free for downloading (OA Articles)
Page 1 /491344
Display every page Item
Comparison between ethanol and hexane for oil extraction from Quercus suber L. fruits
Ferreira-Dias, Suzana,Valente, Dina G.,Abreu, José M.F.
Grasas y Aceites , 2003,
Abstract: The aim of this study was to (i) evaluate the feasibility of replacing n-hexane with ethanol for the extraction of oil from Quercus suber fruits and (ii) optimize, at lab scale, sample preparation and extraction time for both solvents used (n-hexane vs. anhydrous ethanol). For both solvents, the effect of the conditioning process on extraction yield was evaluated. Therefore, a full factorial design was used as a function of four variables: dehulling (with vs. without husks), and thermal treatment of the crushed material (40 oC vs. 75 oC), at different times (5 min vs. 120 min) and pressures (10 kPa vs. 100 kPa). Higher oil yields were obtained with n-hexane when dehulled fruits were conditioned under atmospheric pressure. Better yields were obtained with n-hexane, when dehulled material was treated at 75 oC for 90 min. Ethanol was not adequate for oil extraction from Quercus fruits, since other materials rather than oil were also extracted. El objetivo de este estudio fue (i) evaluar la posibilidad de reemplazar el n-hexano por el etanol para la extracción del aceite de los frutos de Quercus suber y (ii) optimizar, a escala de laboratorio, la preparación de la muestra y el tiempo de extracción para ambos solventes (n-hexano vs. etanol anhidro). Para ambos solventes, se ha evaluado el efecto del proceso de acondicionamiento en el rendimiento de la extracción. Para ello, se ha empleado un dise o factorial completo como función de cuatro variables: descascarillado (con vs sin cascarilla), y tratamiento térmico del material triturado (40 oC vs. 75 oC), a diferentes tiempos (5 min vs. 120 min) y presiones (10 kPa vs. 100 kPa). Los rendimientos más elevados de extracción de aceite se obtuvieron con n-hexano cuando los frutos descascarillados se acondicionaron a presión atmosférica. Cuando el material descascarillado fue tratado a 75 oC por 90 min, se obtuvieron mejores rendimientos con n-hexano. El etanol demostró no ser adecuado para la extracción del aceite de los frutos de Quercus, debido a la extracción conjunta de otros materiales a la vez del aceite.
Pattern recognition of acorns from different Quercus species based on oil content and fatty acid profile
Ferreira-Dias, Suzana,Valente, Dina G.,Abreu, José M.F.
Grasas y Aceites , 2003,
Abstract: The aim of this study was (i) to characterize different species of Quercus genus and (ii) to discriminate among them on the basis of the content and fatty acid composition of the oil in their fruits and/or their morphological aspects via pattern recognition techniques (Principal Component Analysis, PCA, Cluster Analysis, CA, and Discriminant Analysis, DA). Quercus rotundifolia Lam., Quercus suber L. and Quercus pyrenaica Willd., grown in the same stand in the centre of Portugal, were investigated. When oil content and respective fatty acid composition were used to characterize samples, well-separated groups corresponding to each of the species were observed by PCA and confirmed by CA and DA. The a a widtha a and a a lengtha a of acorns exhibited a low discriminant power. Acorns from Q. rotundifolia showed the highest average oil content followed by Q. suber and Q. pyrenaica acorns (9.1, 5.2 and 3.8%, respectively). Fatty acid profiles of Q. rotundifolia and Q. suber oils are similar to olive oil while the oil from Q. pyrenaica acorns is more unsaturated. El objetivo de este estudio fué (i) la caracterización de diferentes especies del género Quercus y (ii) la clasificación de las mismas en base al contenido y composición de ácidos grasos del aceite de sus frutos y/o en sus caracteres morfológicos, via técnicas de patrón de reconocimiento (Análisis de Componentes Principales, ACP, Análisis de Cluster, AC, y Análisis Discriminante, AD). Se han estudiado Quercus rotundifolia Lam., Quercus suber L. y Quercus pyrenaica Willd., pertenecientes a la misma zona del centro de Portugal. Al emplear el contenido de aceite y sus respectivas composiciones de ácidos grasos para caracterizar a las muestras, el ACP reveló grupos bien separados correspondientes a cada especie, los cuales, a su vez, se confirmarón con el AC y el AD. El a a anchoa a y a a longituda a de las bellotas exhibieron un poder discriminante bajo. Las bellotas de Q. rotundifolia mostraron el contenido más elevado de aceite, seguidas de las de Q. suber y Q. pyrenaica (9.1, 5.2 y 3.8%, respectivamente). Los perfiles de ácidos grasos de los aceites de Q. rotundifolia y Q. suber son similares al del aceite de oliva, mientras que el aceite de las bellotas de Q.pyrenaica es más insaturado.
Leaching of a gold bearing partially roasted sulphide. Laboratory scale studies
Almeida, M.F.;
Materials Research , 2001, DOI: 10.1590/S1516-14392001000400014
Abstract: this research aimed at defining a route for recovering precious metals from a very heterogeneous gold bearing sulphide and arsenide concentrate that was partially roasted and dumped by the 1960s when santo antónio mine closed. gold occurs in this concentrate as free particles in the range of 10-100 mm, most of them still enclosed in the pyrite and arsenopyrite matrix. its content varies from 20 to 150 g of au/ton, being higher at the dump upper levels and in the finer concentrate fractions. preliminary tests demonstrated the refractoriness of this product, since the leaching with conventional cyanide solutions and with other leaching solutions gave very low recoveries. however, high concentrated cyanide solutions recover more than 60% of au, although with high nacn and lime consumptions and poor settling characteristics. iron was shown to be highly dissolved in these solutions. some prior treatments clearly favoured the cyanidation process, in particular a roasting step. thus, a large number of roasting experiments was carried out to define the most favourable conditions for recovering gold. however, no clear relationship between roasting conditions and gold dissolution was found due to the heterogeneity of the product and high variance of gold experimental recoveries. these recoveries were calculated considering gold contained in both the leaching residues and leachates, and uncertainties of these results are relatively high. roasting the product at 450-700 °c for 1 h guarantees a high probability to dissolve at least 74% au in a highly concentrated nacn solution stirred for 24 h. the 600-700 °c roasting range is clearly preferable for consuming less cyanide and lime. pre-washing the roasted product seems not to reduce the cyanide consumption. regarding the silver recovery, the nacn and lime consumption are higher while using the products roasted at the lowest tested temperatures. products roasted at higher temperatures have better settling performance.
Challenges in using fish communities for assessing the ecological integrity of non-perennial rivers
M.F Avenant
Water SA , 2010,
Abstract: Environmental Water Assessments (EWAs) aim to protect the ecological integrity of rivers amidst increasing anthropogenic pressures on freshwater resources, and fish communities are the ecosystem component most commonly included. The Fish Response Assessment Index (FRAI) was developed to assess the integrity of fish communities in South African rivers and is commonly applied in EWA studies. This paper reports on the suitability of the FRAI for the non-perennial Seekoei River and discusses some of the challenges faced. Our relatively long and thorough study on the Seekoei River confirmed the concerns that earlier, snapshot, fish integrity assessments in the Orange River system raised: that the existing fish indices are not ideally suited for these rivers with their naturally low species richness and hardy, generalist fish communities. Other difficulties with the use of a score-based method include prediction of the expected species, calculation of a frequency of occurrence rating, selection of the right sampling times for comparative purposes, loss of habitats and sampling points under different flow conditions, and problems experienced when using accumulated data to try to correct for a situation of having too few sampling points. At this stage a more generalised approach is suggested for the Seekoei River, and ultimately other similar non-perennial systems. This could include a number of community characteristics, such as abundance, species richness, species diversity and evenness, recruitment, fish health and the presence/absence of exotic species.
A provisional check list of the reptiles and amphibians of Golden Gate Highlands National Park
M.F. Bates
Koedoe : African Protected Area Conservation and Science , 1991, DOI: 10.4102/koedoe.v34i2.431
Abstract: A provisional check list of 26 reptile and amphibian species (8 frog, 8 lizard and 10 snake species) occurring in Golden Gate Highlands National Park is presented. The list does not reflect the results of an intensive survey, but is a record of specimens collected in the park and preserved at the National Museum, Bloemfontein.
Moraliteit, die opdringerige en die voorwaardelike
M.F. Heyns
Koers : Bulletin for Christian Scholarship , 2010, DOI: 10.4102/koers.v75i1.80
Abstract: Morality, the obtrusive and the conditional The secularist (immanentist), historicist and pluralistic nature of current thinking disables the articulation of transcendental conditions for morality. It is ostensibly especially the constancy of a structure for morality, as transcendental condition, for morality that is disputable. However, an aggressive immanentism sees to it that a transcendent origin for morality does not even appear on the agenda of late modern thinkers, which makes the latter probably an equally serious marginalisation of transcendental considerations. In this article the (sometimes unconscious) experience of some philosophers that a constant structure for morality obtrudes itself upon us, is highlighted. A further claim is that a similar obtrusion can be observed about a coherent diversity of moral sources (i.e. sources which find themselves in a transcendental position with regard to each other). The “most daring” argument is for a transcendental transcendent origin for morality.
De/re/centring of subjective power
M.F. Heyns
Koers : Bulletin for Christian Scholarship , 2000, DOI: 10.4102/koers.v65i1.465
Abstract: The centred self is the self in the centre of the universe with an underlying inner centre; that is, with one of the human abilities as the core power of the human being. I apply this distinction to the meta-psychological theories of Kenneth Gergen and Charles Taylor. Gergen liquidates the autonomous individual only to revert to a centring of the social side of the human condition. It is, according to Gergen, the postmodern condition of advanced transport and communication technologies that will be the end of the authentic self. Gergen rejects the possibility of resisting these postmodern technologies. The upshot of Gergen’s socio-technological determinism is totalitarianism as well as agonism between individual and social aspects. Taylor seemingly steers away from centring one aspect. He nevertheless partially centres intention (interpretation). This gives his de/centring also an undecided and agonistic picture; that is a self in a never-ending conflict with itself and surroundings. I suggest that only a re-centring of all human abilities will avert the final failure of the decentring of the centred self.
Akrasia (swakheid van die wil) en die kontemporêre gesprek oor subjektiwiteit
M.F. Heyns
Koers : Bulletin for Christian Scholarship , 1997, DOI: 10.4102/koers.v62i4.580
Abstract: Akrasia (weakness of will) and the contemporary discourse on subjectivity The issue about akrasia (weakness of the will) concerns the question whether the human will is strong enough to choose and realize actions, or whether a conflict, and a certain type of conflict (i.e. the issue of akrasia), will have the potential to paralyse it. My analysis focuses on ideas of thinkers of the last half of the twentieth century - thinkers like Skinner who practically denies the existence and strength of the se lf and Sartre who postulates a transcendental self with godlike capabilities. I conclude that both leave little room for the idea of akrasia. Akrasia needs a more subtle vision of the power and weakness of the self. To arrive at this conclusion I consider views attempting to reconcile the disempowerment of the se lf by the extra-self with the idea of a self in control of its situation. I argue that these views fail because they assume the akratic conflict to be behi’een the self and extra-self instead of an intra-will conflict. I also deny that the dialectic goal of a fusion o f the self and its situation will give an explanation o f the akratic conflict because dialectics still operate with a centred self which assumes a conflict between the centre and a sub-self periphery. Moreover, this kind of dialectics provides the picture of a permanent victimized self rather than an akratic conflict. I conclude by suggesting the existence of a "dense " self with more subjective capacities than is usually assumed. This, I argue, enhances the scope of, and makes the intra-will conflict more credible.
Declared Knowledge of Beginning Writers.
Morin, M.F.
L1 Educational Studies in Language and Literature , 2005,
Abstract: Most studies of the orthographic development of young writers have largely centred their attention on analyses of written productions. However, an increasing number of researchers are now devoting attention to the information provided by spoken comments made by writers during a production activity. Re- ferred to as metagraphic comments, these utterances give researchers access to young writers’ conceptualizations of written language and the various processes mobilized during a writing task. This article presents the results of a Quebec study aimed at grasping the nature of metagraphic comments and establishing their relationship to writing performance. This research was conducted with 67 French-language subjects who were each given an individual word-writing task at two different moments (at mid-year and year end) in grade one. The analysis of the metagraphic comments, using a grid to categorize them, revealed that young writers have many and varied notions about written French, even at the beginning stages of their schooling. This analysis also led to the observation that comments related to what is thought about language – metalinguistic comments – are much more numerous than those revealing thoughts about cognitive processes at work during the writing activity. Lastly, correlation analyses, which enabled an examination of the relationship between the nature of metagraphic comments and writing performance, suggest that the use of spoken aloud comments during a writing activity does not have the same impact on weak and strong writers.
The politics of invasion and alliance
M.F. Heyns
Koers : Bulletin for Christian Scholarship , 2001, DOI: 10.4102/koers.v66i3.395
Abstract: What should the political priority and relation be between cultural membership, economic concerns and being a citizen of a state? I argue that individualism, economism, and nationalism all harbour the danger of hierarchising these goals with the consequential invasion or even exclusion of one another. I describe both ethnic and state nationalists as using identity to monopolise political concerns. But state or cultural identity is also colonised or marginalised by either individualist or economistic politics. As alternative to invasion politics, I firstly propose that humans should be seen as negotiating with their embedding communities a plurality of identities that reflect a variety of transcendental ways of being human. These identities should then be acknowledged as equal ingredients in the empowerment and make-up of a blossoming human life. The variety of identities should therefore be developed in alliance with each other instead of being the victim of a strategy of mutual invasion or exclusion.
Page 1 /491344
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.