scholarly journals LA “TIERRA”: UN MATERIAL COMPUESTO

2021 ◽  
pp. 167-179
Author(s):  
Juan Carlos Calderón-Peñafiel

La problemática ambiental ha impulsado la investigación de materiales alternativos que ayuden a aminorar el impacto derivado de la construcción. En este contexto, la “tierra” y los materiales a base de arcilla sin cocer se han presentado como una alternativa interesante a materiales convencionales que incorporan gran cantidad de energía. Pese a que existe una creencia generalizada de que la “tierra” y los materiales a base de arcilla cruda están bien entendidos, mediante el estudio del estado del arte en lo referente a los antecedentes  históricos, los limitantes, la innovación del material, sus características y composición, se expone la complejidad que conlleva su estudio y correcta aplicación. Se puede decir que “tierra” es un nombre genérico que se da al material compuesto por diferentes tipos de silicatos. Estos minerales tienen características y propiedades específicas de acuerdo a su estructura y composición química molecular. Entre los silicatos, las arcillas contienen nanopartículas responsables de conglomerar el resto de constituyentes gracias a sus características y, por tanto, son consideradas componentes fundamentales para la exploración e innovación del material. En la actualidad la combinación de modernas técnicas de análisis permite una mayor comprensión de la composición y estructura de la “tierra” y la arcilla. Estos avances han provocado el desarrollo de tecnologías que permiten optimizar los materiales de arcilla tomando en cuenta las características microscópicas mediante procesos microbiológicos; nanotecnología, geopolimerización, activación alcalina, etc.Palabras clave: Construcción con tierra, tierra, arcilla, innovación, composición. AbstractThe environmental problem has prompted research into alternative materials that help reduce the impact from construction. In this context, soil and raw clay-based materials have emerged as an interesting alternative to conventional materials that incorporate a large amount of energy. Although there is a widespread belief that soil and raw clay-based materials are well understood, through the study of the state of the art in relation to the historical background, the limitations, the innovation of the material, its characteristics andcomposition, the complexity involved in its study and correct application is exposed. It can be said that soil is a generic name given to the material composed of different types of silicates. These minerals have specific characteristics and properties according to their structure and molecular chemical composition. Among the silicates, clays contain nanoparticles responsible for conglomerating the rest of the constituents thanks to their characteristics and, therefore, they are considered fundamental components for the exploration andinnovation of the material. Nowadays, the combination of modern analysis techniques allows a better understanding of the composition and structure of soil and clay. These advances have led to the development of technologies that allow the optimization of clay materials taking into account the microscopic characteristics through microbiological processes; nanotechnology, geopolymerization, alkaline activation, etc.Keywords: Construction with soil, soil, clay, innovation, composition.

Author(s):  
Wendy J. Schiller ◽  
Charles Stewart

This chapter integrates findings on indirect elections with current scholarship on the impact of the adoption of the Seventeenth Amendment and onset of direct elections. It constructs a comprehensive counterfactual analysis that helps demonstrate what the political outcomes would have been with direct elections in place since the founding, and in contrast, what Senate elections would look like after 1913 if indirect elections were still in place. It also addresses the question of whether U.S. senators represented states as units and responded to state governmental concerns more under the indirect system than they do under direct elections. It argues that indirect election had little impact on the Senate's overall partisan composition prior to 1913. Contrary to widespread belief, had direct election been in effect during the years immediately preceding the Seventeenth Amendment's passage, Republicans, not Democrats, would have benefited.


Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1581
Author(s):  
Rafał Babilas ◽  
Monika Spilka ◽  
Katarzyna Młynarek ◽  
Wojciech Łoński ◽  
Dariusz Łukowiec ◽  
...  

The effect of iron and yttrium additions on glass forming ability and corrosion resistance of Al88Y8-xFe4+x (x = 0, 1, 2 at.%) alloys in the form of ingots and melt-spun ribbons was investigated. The crystalline multiphase structure of ingots and amorphous-crystalline structure of ribbons were examined by a number of analytical techniques including X-ray diffraction, Mössbauer spectroscopy, and transmission electron microscopy. It was confirmed that the higher Fe additions contributed to formation of amorphous structures. The impact of chemical composition and structure of alloys on their corrosion resistance was characterized by electrochemical tests in 3.5% NaCl solution at 25 °C. The identification of the mechanism of chemical reactions taking place during polarization test along with the morphology and internal structure of the surface oxide films generated was performed. It was revealed that the best corrosion resistance was achieved for the Al88Y7Fe5 alloy in the form of ribbon, which exhibited the lowest corrosion current density (jcorr = 0.09 μA/cm2) and the highest polarization resistance (Rp = 96.7 kΩ∙cm2).


2006 ◽  
Vol 514-516 ◽  
pp. 1116-1120 ◽  
Author(s):  
M.Fátima Cerqueira ◽  
Margarita Stepikhova ◽  
Maria Losurdo ◽  
Teresa Monteiro ◽  
Manuel J. Soares ◽  
...  

Erbium doped nanocrystalline silicon thin films were produced by reactive magnetron r.f. sputtering. Their structural and chemical properties were studied by micro-Raman, spectroscopic ellipsometry and Rutherford backscattering spectroscopy. Films with different crystalline fraction and crystallite size were deposited by changing the deposition parameters. The impact of the composition and structure of Erbium ions environment on the 1.5 µm photoluminescence is discussed.


2017 ◽  
Author(s):  
Arab World English Journal ◽  
Sana SAKALE

Instruction plays a major role in the development of speaking skills for second language learners. Different approaches and methods have emerged throughout the history of language learning/teaching based on the influence of different theories of language, psychology, and related domains such as psycholinguistics, sociolinguistics, pragmatics and cultural studies. Two major trends in language teaching emerged under the influence of these mentioned language theories, namely, accuracy based versus fluency based approaches. This article gives a historical sketch up to these trends in an attempt to provide a historical background and to empirically bring evidence that wait time instruction and teaching experience can impact classroom feedback in Moroccan classes. Relevant questions related to the role of teachers’ experience in leading different types of feedback, the effect of the number of teaching years as well as the correlation between wait time instruction and the corresponding teaching experience are closely investigated. This article adheres to a mixed design or what has been identified in research methodology as ex-post facto (Cohen, Manion, Morrison, 2007). Therefore, it is both a qualitative and a descriptive one. For the type of instructions used, the results obtained show the insignificance of the impact of experience on this variable. On the other hand, results retained that wait- time instruction in comparison to other items recorded a higher significance of the impact of experience. Therefore, current article brings empirical evidence on how wait- time instruction plays a crucial role in spoken activity for second language learners.


Author(s):  
Marco Antonio Peña ◽  
Patricio Calderón

This study assessed the impact produced by a wildfire and an infectious outbreak led by an oomycete pseudofungi, both occurred in 2015, on the state of Araucaria-Lenga forests of the China Muerta Reserve, placed in the southern Andes of Chile. To do this, a greenness vegetation spectral index was calculated over a multitemporal set of Landsat-8 images, acquired biannually on near-anniversary dates, which was subject to subtractions between ex-ante (2013) and ex-post dates (2015, 2017, 2019). Results show the magnitude and temporal progression of both disturbances, highlighting the celerity and aggressiveness of the wildfire. Although the affected vegetation land covers currently show values close to the recovery of the primal biomass, the inclusion of field-based data to deepen the possible composition and structure variations of these forests is needed.


2021 ◽  
Author(s):  
◽  
Rosina Hickman

<p>Home movies are now viewed in a variety of public contexts, a shift that entails a loss of their original meanings. In order to consider the impact of exhibiting these private documents, this thesis analyses the use of home movies within recycled footage productions, archival curation and online video-sharing. Investigating a variety of formal and informal screening contexts through close readings and archival research, it asks: what meanings do home movies acquire in new contexts? How might the reuse of home movies affect our understandings of their production and the past they portray? Does a perception that home movies could appear boring influence how they are framed or altered for public audiences?  Due to their form and content, home movies may seem ill-suited to public exhibition. Popular discourses about home movies during their heyday of production reveal a widespread belief that they were boring (for outsiders) to watch. While recent literature has assessed home movies more favourably, it has tended to overlook their potential to bore viewers who have no personal relationship to them. Drawing upon theories of boredom, this study argues meaningfulness is the principal factor determining whether a viewer finds a particular film interesting or boring. In their original form, home movies may appear relatively meaningless and therefore boring to public audiences. Recycled footage films re-edit images, however, to create engaging viewing experiences through narrative and affect. While more experimental productions frequently question the evidential value of home movie images, television documentaries tend to encourage audiences to perceive footage as authentic or nostalgic. Narrative and affect also feature in the exhibition strategies of moving image archives. Curated public programmes provide informative and enjoyable viewing for general audiences, but almost inevitably promote certain understandings of the past by offering specific interpretations of selected films. Moreover, the affective appeal of home movie images may outweigh other forms of meaning for viewers, particularly in community or participatory screening contexts. Online video-sharing platforms such as YouTube, which are curated by algorithms rather than human expertise, feature numerous home movies without any kind of framing or description. While this might seem profoundly boring, viewer comments suggest meaninglessness can foster imaginative and empathetic responses to home movies, often expressed as nostalgic longing. This propensity of home movie footage within different screening contexts to encourage nostalgic sentiments, or a belief that life was better in the past, has implications for collective memory and understandings of history. Moreover, the ability of at least some viewers to enjoy home movies in relatively contextless spaces suggests that in certain instances qualities associated with boredom may not be a significant impediment to meaningful experience after all.</p>


2015 ◽  
pp. 1308-1330
Author(s):  
Howard Menand

The chapter applies critical theory to analyze the impact of globalization on education at the classroom level. Based on the hypothesis that education policy decisions made at the global level result in outcomes at the classroom level, it is clear globalization directly impacts students in the classroom. Therefore, within the context of curriculum and instruction, this chapter critically explores 21st century instructional practices as a response to the following research question: What are effective methods for engaging all learners in today's classrooms? The chapter incorporates qualitative research results and historical background about globalization, which thus situates current 21st century instructional practices within a framework for critical deconstruction. Finally, the qualitative research utilized in this chapter stems from classroom observations of teachers delivering 21st century instruction, and this research serves the purpose of clearly illustrating the characteristics of 21st century instruction in the classroom.


Land ◽  
2019 ◽  
Vol 8 (8) ◽  
pp. 122 ◽  
Author(s):  
Meyer ◽  
Holloway ◽  
Christiansen ◽  
Miller ◽  
D’Odorico ◽  
...  

Savannas are extremely important socio-economic landscapes, with pastoralist societies relying on these ecosystems to sustain their livelihoods and economy. Globally, there is an increase of woody vegetation in these ecosystems, degrading the potential of these multi-functional landscapes to sustain societies and wildlife. Several mechanisms have been invoked to explain the processes responsible for woody vegetation composition; however, these are often investigated separately at scales not best suited to land-managers, thereby impeding the evaluation of their relative importance. We ran six transects at 15 sites along the Kalahari transect, collecting data on species identity, diversity, and abundance. We used Poisson and Tobit regression models to investigate the relationship among woody vegetation, precipitation, grazing, borehole density, and fire. We identified 44 species across 78 transects, with the highest species richness and abundance occurring at Kuke (middle of the rainfall gradient). Precipitation was the most important environmental variable across all species and various morphological groups, while increased borehole density and livestock resulted in lower bipinnate species abundance, contradicting the consensus that these managed features increase the presence of such species. Rotating cattle between boreholes subsequently reduces the impact of trampling and grazing on the soil and maintains and/or reduces woody vegetation abundance.


2020 ◽  
Vol 287 (1927) ◽  
pp. 20192945 ◽  
Author(s):  
Cristina M. Herren

The strength of biotic interactions within an ecological community affects the susceptibility of the community to invasion by introduced taxa. In microbial communities, cross-feeding is a widespread type of biotic interaction that has the potential to affect community assembly and stability. Yet, there is little understanding of how the presence of cross-feeding within a community affects invasion risk. Here, I develop a metabolite-explicit model where native microbial taxa interact through both cross-feeding and competition for metabolites. I use this model to study how the strength of biotic interactions, especially cross-feeding, influence whether an introduced taxon can join the community. I found that stronger cross-feeding and competition led to much lower invasion risk, as both types of biotic interactions lead to greater metabolite scarcity for the invader. I also evaluated the impact of a successful invader on community composition and structure. The effect of invaders on the native community was greatest at intermediate levels of cross-feeding; at this ‘critical’ level of cross-feeding, successful invaders generally cause decreased diversity, decreased productivity, greater metabolite availability, and decreased quantities of metabolites exchanged among taxa. Furthermore, these changes resulting from a successful primary invader made communities further susceptible to future invaders. The increase in invasion risk was greatest when the network of metabolite exchange between taxa was minimally redundant. Thus, this model demonstrates a case of invasional meltdown that is mediated by initial invaders disrupting the metabolite exchange networks of the native community.


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