Slave-Boson Three-Band Model with O-O Hopping for High-Tc Superconductors

Slave boson mean-field approximation is carried out analytically for weakly doped CuO_2 conduction planes, characterized by Cu-O charge transfer energy \Delta_{pd}, Cu-O hopping t_0, O-O hopping t' and repulsion U_d between holes on Cu site taken as infinite. At zero doping \delta, finite negative t',|t'|<t_0/2, expands the range of stability of the covalent, conducting state on the expense of the insulating state which, however, remains stable at larger \Delta_{pd}. For sufficiently large \Delta_{pd} the renormalized charge transfer energy saturates at 4|t'| instead of decreasing to zero, as at t'=0 case. In contrast to t', finite \delta suppresses the insulating state nearly symmetrically with respect to the sign of \delta. The regime with charge transfer energy renormalized close to 4|t'| fits remarkably well the ARPES spectra of Bi2212 and LSCO, and, in the latter case, explains the observed strong doping dependence of the Cu-O hopping.Comment: 4 pages, 2 figure

Tribological Characterisation of Graphene Oxide as Lubricant Additive on Hypereutectic Al-25Si/Steel Tribopair

The performance of a lubricant greatly depends on the additives it involves. However, recently used additives produce severe pollution when they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide (GO) is considered to be environmentally friendly. The scope of this study is to explore the fundamental tribological behavior of graphene, the first existing 2D material, and evaluate its performance as a lubricant additive. The friction and wear behavior of 0.5 wt% concentrations of GO particles in ethanol and SAE20W50 engine oil on a hypereutectic Al-25Si alloy disc against steel ball was studied at 5 N load. GO as an additive reduced the wear coefficient by 60–80% with 30 Hz frequency for 120 m sliding distance. The minimum value of the coefficient of friction (0.057) was found with SAE20W50 + 0.5 wt% GO. A possible explanation for these results is that the graphene layers act as a 2D nanomaterial and form a conformal protective film on the sliding contact interfaces and easily shear off due to weak Van der Waal's forces and drastically reduce the wear. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Raman spectroscopy were used for characterization of GO and wear scars

“Because we felt annoyed”. Emotions in the production of the political action of children that live in an occupied house

El pensamiento moderno se ha configurado en dicotomías como adultez/infancia y pensar/sentir, que se sintetizan en una división permanente entre lo racional y lo irracional desde donde se ha analizado la acción humana. Sin embargo, la antropología ha desarrollado diversas líneas de trabajo que problematizan estos esquemas aportando otras miradas sobre la niñez y sobre la movilización política. En este mismo sentido, y a partir de un extenso estudio etnográfico, nos proponemos analizar los modos en los que los/as niños/as de entre 8 y 15 años que viven en una casa tomada de la Ciudad de Buenos Aires producen acciones políticas colectivas enraizadas en sus emociones compartidas.Modern thought has been configured in dichotomies such as adulthood/infancy and thinking/feeling, which are synthesized in a permanent division between the rational and the irrational from where human action has been analyzed. However, anthropology has developed several lines of work that problematize these schemes providing alternative views on childhood and on political mobilization. In this same sense, and from an extensive ethnographic study, we propose to analyze the ways in which children between the ages of 8 and 15 living in an occupied house from the City of Buenos Aires produce collective political actions rooted in their shared emotions.Fil: Shabel, Paula Nurit. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires; Argentin

"Aprendo lo que se me canta". Niños/as frente a diversas propuestas de construcción de conocimiento

El objeto de estudio de la presenteinvestigación son las actitudesque adoptan los/as niños/as grandesde AulaVereda (AV) frente a las actividadesque les proponen un proceso deenseñanza y aprendizaje sobre subarrio en el contexto específico dela escuelita. En AV se han identificadoactitudes de los/as niños/asde mayor o menor interés y participaciónen las actividades deltaller del barrio propuestas por los/as profes que generan aprendizajesmás o menos significativosen los educandos y trataremos acontinuación de explicar los porqué. Definimos actitud como ?unaorganización durable de procesosmotivacionales, sentimientosemocionales, percepciones y aspectoscognitivos relacionadoscon una parte del mundo social?(Sirvent, 1999: 126) y así intentaremosexplicar las razones por lascuales ciertos ejercicios del tallerconvocan a los/as niños/as másque otros. Entendemos que estetrabajo puede contribuir a pensarfuturas intervenciones pedagógicascon niños y niñas que respetenlos intereses y las necesidades delos/as educandos sin perder devista la intencionalidad de los/aseducadores/as en relación con superspectiva de derechos.Fil: Shabel, Paula Nurit. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

“Nada tem mudado”: Práticas de um feminismo inter-geracional durante o confinamento

La crisis económica, sanitaria y humana que desató la pandemia de covid-19 profundizó desigualdades que se encarnaron especialmente en ciertos cuerpos feminizados y personas que viven en condiciones de hacinamiento, para quienes permanecer recluidos en el espacio privado representa un riesgo. El objetivo de este trabajo es analizar la experiencia de la pandemia que tuvieron niñas y adolescentes que viven una situación de precariedad habitacional en la Ciudad de Buenos Aires y que participan de la organización social La Caldera. Desde un trabajo etnográfico, estudio las creativas formas de encuentro generadas tanto por las adultas como por las niñas de la organización para abordar las situaciones de violencia y los modos en que dichos encuentros tensionaron las categorías público-privado-íntimo para darle lugar a una práctica feminista en clave intergeneracional fundada en una forma de cuidado no adultista que denomino “amistad”.The economic, health and human crisis triggered by the Covid-19 pandemic exacerbated inequalities that were particularly embodied in certain feminized bodies and people living in crowded conditions, for whom being confined in private space poses a risk. The purpose of this article is to analyze the experience of the pandemic undergone by girls and female adolescents in precarious living conditions in the City of Buenos Aires, who participated in the La Caldera social organization. From an ethnographic perspective, I study the creative types of encounter devised by both adult women and girls in the organization to address situations of violence and the ways these encounters stretched the limits of public-private-intimate categories to give rise to an intergenerational feminist practice based on a non-adult form of care I call friendship.A crise econômica, de saúde e humana que desencadeou a pandemia de Covid-19 aprofundou as desigualdades, incorporadas especialmente em certos corpos feminizados e pessoas que vivem em condições de superlotação, para quem permanecer confinado em espaço privado representa um risco. O objetivo deste trabalho é analisar a experiência de pandemia de meninas e adolescentes que vivem em situação precária de moradia na Cidade de Buenos Aires e que participam da organização social La Caldera. A partir dum trabalho etnográfico, estudo as formas criativas de encontro geradas tanto pelas adultas quanto pelas meninas da organização para enfrentar situações de violência e as formas como esses encontros alteraram as categorias público-privado-íntimo para dar origem a uma prática feminista inter-geracional fundada numa forma de cuidado não adulto que chamo de amizade.Fil: Shabel, Paula Nurit. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires; Argentin

Treatise on teratos-pedagogy: a queer analysis of teachers and students at school

El objetivo del presente artículo es presentar las ideas fundamentales de las teorías cuir para hacerlas dialogar con las problemáticas de nuestras escuelas cotidianas y contribuir así con una pedagogía para la creación de un espacio público que produzca igualdad y la posibilidad de generar comunidad desde la diferencia. Apelando a la figura de lo monstruoso (en griego teratos), como tópico recurrente en los universos cuir, realizaremos un análisis en dos partes: primero radicalizando la otredad de lxs estudiantes niñxs en tanto anormalidad no/anti/pre-humana y, segundo, comparando la práctica docente con dos criaturas teratológicas como son Frankenstein y las brujas. A partir de una metodología cualitativa de discusión conceptual, forjamos una narrativa teratológica que nos permite explorar diversas dimensiones de la vida en las aulas, nombrar los conflictos de forma inesperada y, quizás, des-cubrir alternativas de acción educativa.The aim of this article is to present the fundamental ideas of queer theories in order to make them dialogue with the problems of our everyday schools and, thus, contribute to a pedagogy for the creation of a public space that produces equality and the possibility of generating community from difference. Appealing to the figure of the monstrous (in Greek tératos), as a recurrent topic in the queer universes, we will carry out an analysis in two parts: first, radicalising the otherness of the children students as a non-/anti/pre-human abnormality and, second, comparing the teaching practice with two teratological creatures, such as Frankenstein and the witches. Using a qualitative methodology of conceptual discussion, we forge a teratological narrative that allows us to explore various dimensions of classroom life, to name conflicts in unexpected ways and, perhaps, to uncover alternatives for educational action.Fil: Shabel, Paula Nurit. Consejo Nacional de Investigaciones Científicas y Técnicas. Universidad de Buenos Aires; Argentin

A alteridade da idade

Este trabajo de reflexión teórica y análisis bibliográfico tiene como objetivo estudiar el modo en que Occidente ha configurado la alteridad en su dimensión etaria. A partir de los estudios queer/cuir y una revisión de la noción de otredad temporal desarrollada por el antropólogo Johannes Fabian, se sostiene como hipótesis que la noción de tiempo acumulativo ha normalizado las etapas vitales al servicio de la productividad del capital, otorgándole el monopolio del presente a un solo grupo −el adulto– y desplazando hacia el pasado a la vejez y hacia el futuro a la infancia, negando su existencia actual y forjando marcos temporales que definen lo que es ser humano. Cierra el trabajo un llamado a la democratización etaria del presente y una pregunta por la invención de un tiempo vital diferente en el que no necesitemos medir los años de un cuerpo para reconocerlo como un humano completo y un igual.The aim of this theoretical reflection and bibliographical analysis is to study the way in which Western societies have created otherness in its age dimension. Based on queer studies and a review of the notion of temporal otherness developed by the anthropologist Johannes Fabian, it explores the hypothesis that the notion of cumulative time has standardised the stages of life at the service of capital productivity, granting a monopoly of the present to a single group −the adult- and displacing old age into the past and childhood into the future, denying its current existence and forging temporal frameworks that define what it is to be human. The work closes with a call for the age democratisation of the present and a question about the invention of a different vital time in which we do not need to measure the years of a body to recognise it as as a full human being and an equal.O objetivo desta reflexão teórica e análise bibliográfica é estudar a maneira pela qual sociedades ocidentais construíram a alteridade em sua dimensão etária. Com base nos estudos queer/cuir e em uma revisão da noção de alteridade temporal desenvolvida por o antropólogo Johannes Fabian, levanta-se a hipótese de que a noção de tempo cumulativo normalizou os estágios da vida a serviço da produtividade do capital, concedendo o monopólio do presente a um único grupo - o adulto - e deslocando a velhice para o passado e a infância para o futuro, negando sua existência atual e forjando estruturas temporais que definem o que é ser humano. O trabalho termina com um apelo à democratização da idade do presente e uma pergunta sobre a invenção de um tempo vital diferente, no qual não precisamos medir os anos de um corpo para reconhecê-lo como um ser humano pleno e igual

Bidirectional switch of the valence associated with a hippocampal contextual memory engram

The valence of memories is malleable because of their intrinsic reconstructive property. This property of memory has been used clinically to treat maladaptive behaviours. However, the neuronal mechanisms and brain circuits that enable the switching of the valence of memories remain largely unknown. Here we investigated these mechanisms by applying the recently developed memory engram cell- manipulation technique. We labelled with channelrhodopsin-2 (ChR2) a population of cells in either the dorsal dentate gyrus (DG) of the hippocampus or the basolateral complex of the amygdala (BLA) that were specifically activated during contextual fear or reward conditioning. Both groups of fear-conditioned mice displayed aversive light-dependent responses in an optogenetic place avoidance test, whereas both DG- and BLA-labelled mice that underwent reward conditioning exhibited an appetitive response in an optogenetic place preference test. Next, in an attempt to reverse the valence of memory within a subject, mice whose DG or BLA engram had initially been labelled by contextual fear or reward conditioning were subjected to a second conditioning of the opposite valence while their original DG or BLA engram was reactivated by blue light. Subsequent optogenetic place avoidance and preference tests revealed that although the DG-engram group displayed a response indicating a switch of the memory valence, the BLA-engram group did not. This switch was also evident at the cellular level by a change in functional connectivity between DG engram-bearing cells and BLA engram-bearing cells. Thus, we found that in the DG, the neurons carrying the memory engram of a given neutral context have plasticity such that the valence of a conditioned response evoked by their reactivation can be reversed by re-associating this contextual memory engram with a new unconditioned stimulus of an opposite valence. Our present work provides new insight into the functional neural circuits underlying the malleability of emotional memory.RIKEN Brain Science InstituteHoward Hughes Medical InstituteJPB FoundationNational Institutes of Health (U.S.) (Pre-doctoral Training Grant T32GM007287

“Venimos a jugar y a luchar”. Participación política de niños y niñas en organizaciones sociales

La vuelta de la democracia en la Argentina permitió un avance en materia de derechos que, en el campo de la niñez, se materializó en un cambio legislativo profundo y en la constitucionalización de la Convención sobre los Derechos del Niño. Sin embargo, estas modificaciones formales no significaron siempre una mejora real en las vidas de los niños, sobre todo en escenarios de desigualdad y creciente polarización como es el caso del Área Metropolitana de Buenos Aires (AMBA). Frente a esta situación diversas organizaciones sociales y políticas han desarrollado experiencias de lucha por una infancia digna con los propios niños como protagonistas. El objetivo de la presente investigación es analizar las formas de participación infantil que propusieron y llevaron adelante diez de estas organizaciones en el proceso de construcción del Encuentro Nacional de Niñez de 2015. Ahondaremos, particularmente, en el lugar que ocupa el juego en estos discursos y prácticas participativas. Para ello desarrollamos un estudio etnográfico en el espacio de coordinación y debate de estas organizaciones, a la que asisten tanto adultos como niñxs. Además, realizamos entrevistas individuales y colectivas a los adultos y niñxs que participan de dichas instituciones.The re-democratization process in Argentina encouraged an improvement in the human rights field that, regarding childhood issues, meant a deep legislative change and the incorporation of the Convention on the Rights of the Children in the national Constitution. However, these law modifications were not always translated in better living conditions for children, specially, in contexts of inequality and increasing social polarization, as it is the Metropolitan Area of Buenos Aires (AMBA). To counteract this situation, different social and political organizations have developed experiences to struggle for a dignified childhood considering children as main characters of the action. In this scenario, the aim of this research is to analyze the ways in which these social organizations proposed and carried on the children political participation in the planning and making of the National Childhood Convention in 2015. We will study, particularly, how games are used in both, the speeches and practices of children political participation. In order to reach our goals, we made an ethnographic study in the coordination meetings where children and adults prepared the Convention. Additionally, we produced individual and collective interviews to both, children and adults that participate in the social organizations.Fil: Shabel, Paula Nurit. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Instituto de Ciencias Antropológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin