Cultura escolar e sua relação com o saber matemático: os sentidos da docência revelados nos cadernos de anotações de uma professora primária

In this article, aspects of the educational, cultural and social memory of the Brazilian Northeastern hinterland are analyzed, using the notebooks of primary teachers as a research source to understand the teaching of mathematics developed in the early years of elementary school in the period between 1950 and 1990. School notebooks make it possible to produce knowledge because it contains stories, socioeconomic, political, cultural and educational contexts created in different time periods. The aim of this study is to identify the content covered in the school and aspects related to elementary knowledge of mathematics. School notebooks allow us to produce knowledge because they contain historical, socioeconomic, political, cultural and educational contexts which were gestated in different time periods. The goal is to identify the contents covered and aspects related to elementary knowledge of mathematics. As theoretical references were adopted the understanding of Viñao Frago (2008) about school culture and the concept of Bernard Charlot (2000; 1996) about relationship with knowledge that brings the notion of relationship understood as a set of meanings and space for the subject's activities, inscribed at a certain time. Adopting Cultural History as a theoretical-methodological framework based on the propositions of Roger Chartier (1990) and considering research in the context of the history of school subjects, undertaken by André Chervel (1990), the text still considers Carlo Ginzburg's evidential paradigm (1989), in the search for representing the past and the present of mathematical education in teacher education.En este artículo se analizan aspectos de la memoria educativa, cultural y social del hinterland nororiental brasileño, teniendo como fuente primaria de investigación los cuadernos de apuntes de maestros de primaria para comprender la enseñanza de las matemáticas desarrollada en los primeros años de la escuela primaria en el período. entre 1950 y 1990. Los cuadernos escolares permiten producir conocimiento porque contienen historias, contextos socioeconómicos, políticos, culturales y educativos generados en diferentes momentos. El objetivo de este estudio es identificar los contenidos cubiertos en la escuela y los aspectos relacionados con los conocimientos elementales de la matemática. Como referentes teóricos se adoptaron el concepto de cultura escolar defendido por Viñao Frago (2008) y el concepto de relación con el conocimiento de Bernard Charlot (2000; 1996) que trae la noción de relación entendida como un conjunto de significados y espacio de actividades del sujeto, inscrito en un tiempo. Adoptando la Historia Cultural como marco teórico-metodológico a partir de las proposiciones de Roger Chartier (1990) y considerando la investigación en el contexto de la historia de las asignaturas escolares, realizada por André Chervel (1990), el texto sigue considerando el paradigma de acusación de Carlo Ginzburg (1989), en la búsqueda de la representación del pasado y presente de la educación matemática en la formación del profesorado.Nesse artigo são analisados aspectos da memória educativa, cultural e social do sertão nordestino brasileiro, tendo como fonte de pesquisa os cadernos de anotações de professores primários para compreender o ensino de matemática desenvolvido nos anos iniciais do ensino fundamental no período compreendido entre 1950 e 1990. Os cadernos escolares permitem produzir conhecimentos por conter histórias, contextos socioeconômicos, políticos, culturais e educacionais gestados em temporalidades diversas. O objetivo deste estudo é identificar os conteúdos abordados na escola e aspectos relacionados aos saberes elementares de matemática. Como referências teóricas foram adotadas a concepção de cultura escolar defendida por Viñao Frago (2008) e o conceito de relação com o saber de Bernard Charlot (2000; 1996) que traz a noção de relação entendida como conjunto de significados e espaço de atividades do sujeito, inscritos num tempo. Adotando como referencial teórico-metodológico a História Cultural a partir das proposições de Roger Chartier (1990) e considerando as pesquisas no âmbito da história das disciplinas escolares, empreendidas por André Chervel (1990), o texto ainda considera o paradigma indiciário, de Carlo Ginzburg (1989), na busca da representação do passado e do presente da educação matemática na formação de professores

Impact of Structural Health Monitoring on Aircraft Operating Costs by Multidisciplinary Analysis

Structural health monitoring is recognized as a viable solution to increase aviation safety and decrease operating costs enabling a novel maintenance approach based on the actual condition of the airframe, mitigating operating costs induced by scheduled inspections. However, the net benefit is hardly demonstrated, and it is still unclear how the implementation of such an autonomic system can affect performance at aircraft level. To close this gap, this paper presents a systematic analysis where the impact of cost and weight of integrating permanently attached sensors-used for diagnostics- affect the main performance of the aircraft. Through a multidisciplinary aircraft analysis framework, the increment of aircraft operating empty weight is compared with the possible benefits in terms of direct operating costs to identify a breakeven point. Furthermore, the analysis allows to establish a design guideline for structural health monitoring systems returning a safer aircraft without any economic penalties. The results show that the operating costs are lower than those of the reference aircraft up to 4% increase in maximum take-off weight. Paper findings suggest to considering a condition monitoring strategy from the conceptual design stage, since it could maximize the impact of such innovative technology. However, it involves in a design of a brand-new aircraft instead of a modification of an existing one

Potential Benefit of Structural Health Monitoring System on Civil Jet Aircraft

Structural health monitoring represents an interesting enabling technology towards increasing aviation safety and reducing operating costs by unlocking novel maintenance approaches and procedures. However, the benefits of such a technology are limited to maintenance costs reductions by cutting or even eliminating some maintenance scheduled checks. The key limitation to move a step further in exploiting structural health monitoring technology is represented by the regulation imposed in sizing aircraft composite structures. A safety margin of 2.0 is usually applied to estimate the ultimate loading that composite structures must withstand. This limitation is imposed since physical nondestructive inspection of composite structures is really challenging or even impossible in some cases. However, a structural health monitoring system represents a viable way for a real time check for the health status of a composite structure. Thus, the introduction of structural health monitoring should help into reducing the stringent safety margin imposed by aviation regulation for a safe design of composite structures. By assuming a safety margin reduction from 2.0 to 1.75 thanks to the installation of permanently attached sensors for structural health diagnostics, this paper assesses the potential fuel savings and direct operating costs through a multidisciplinary analysis on a A220-like aircraft. According to the foreseen level of technology, addressed through the number of sensors per square meter, a DOC saving from 2% up to 5% is achievable preserving, at the same time, all the key aircraft performance

Growth-Induced Strain in Chemical Vapor Deposited Monolayer MoS2: Experimental and Theoretical Investigation

Monolayer molybdenum disulphide (MoS$_2$) is a promising two-dimensional (2D) material for nanoelectronic and optoelectronic applications. The large-area growth of MoS$_2$ has been demonstrated using chemical vapor deposition (CVD) in a wide range of deposition temperatures from 600 {\deg}C to 1000 {\deg}C. However, a direct comparison of growth parameters and resulting material properties has not been made so far. Here, we present a systematic experimental and theoretical investigation of optical properties of monolayer MoS$_2$ grown at different temperatures. Micro-Raman and photoluminescence (PL) studies reveal observable inhomogeneities in optical properties of the as-grown single crystalline grains of MoS$_2$. Close examination of the Raman and PL features clearly indicate that growth-induced strain is the main source of distinct optical properties. We carry out density functional theory calculations to describe the interaction of growing MoS$_2$ layers with the growth substrate as the origin of strain. Our work explains the variation of band gap energies of CVD-grown monolayer MoS$_2$, extracted using PL spectroscopy, as a function of deposition temperature. The methodology has general applicability to model and predict the influence of growth conditions on strain in 2D materials.Comment: 37 pages, 6 figures, 10 figures in supporting informatio

Ultra Low Specific Contact Resistivity in Metal-Graphene Junctions via Atomic Orbital Engineering

A systematic investigation of graphene edge contacts is provided. Intentionally patterning monolayer graphene at the contact region creates well-defined edge contacts that lead to a 67% enhancement in current injection from a gold contact. Specific contact resistivity is reduced from 1372 {\Omega}m for a device with surface contacts to 456 {\Omega}m when contacts are patterned with holes. Electrostatic doping of the graphene further reduces contact resistivity from 519 {\Omega}m to 45 {\Omega}m, a substantial decrease of 91%. The experimental results are supported and understood via a multi-scale numerical model, based on density-functional-theory calculations and transport simulations. The data is analyzed with regards to the edge perimeter and hole-to-graphene ratio, which provides insights into optimized contact geometries. The current work thus indicates a reliable and reproducible approach for fabricating low resistance contacts in graphene devices. We provide a simple guideline for contact design that can be exploited to guide graphene and 2D material contact engineering.Comment: 26 page

Design Evolution and Wind Tunnel Tests of a Three-Lifting Surface Regional Transport Aircraft

This paper deals with the experimental assessment of the aerodynamic characteristics of an innovative large turboprop aircraft. The configuration is a three-lifting surfaces airplane with rear engine installation at tail tips, conceived to carry up to 130 passengers and targeting a minimum economic and environmental impact, which is competitive with regional jets on short and medium hauls. The three-lifting surfaces layout is the output of previous research made by the authors, and it has been selected to fully comply with the market and design constraints. An experimental test campaign was required to validate the aerodynamics, stability, and control of this innovative configuration. From the results of the first campaign, it appeared that the aircraft had insufficient longitudinal and directional stability. Thus, the authors worked to improve these characteristics, updating the design and executing a second wind tunnel test campaign. The evolution of the design is described in the first part of the paper. In the second part, the authors discuss the aerodynamic interference effects among aircraft components, detailing how the combined downwash coming from both the canard and wing, as well as their wakes, affects the empennage aerodynamics. Experimental tests have revealed a significant reduction of the longitudinal stability due to canard additional downwash, especially at low attitudes. Furthermore, it was found that the canard generates a non-linearity on the aircraft directional stability derivative at moderate sideslip angles because of its tip vortex impinging on the vertical tail. Despite the detrimental interference due to the canard, the updated aircraft proved to be statically stable with sufficient margin at the most rearward center of gravity. Lessons learned in this research may be useful to aerodynamicists and aircraft designers facing similar issues

Directional Stability Issues of a Three Lifting Surface Aircraft

This paper deals with the evaluation of the interference effects among aircraft components in a three lifting surface configuration, an innovative layout for a high-capacity turboprop (130 pax), which is supposed to be competitive with respect to short/medium haul regional jets. The feasibility study of such a configuration is framed within the Innovative turbopROp configuratioN (IRON) project. An experimental wind tunnel test campaign has been performed on a 1:25 scaled model at the main subsonic wind tunnel facility of the Industrial Engineering Department of the University of Naples Federico II. Beside the well-known detrimental effects of the angle of attacK on the sidewash, the experimental tests have highlighted a strong directional stability reduction due to the canard interference with both the fuselage and the vertical tail. Results have shown that the canard increases the fuselage instability of about 14%. The canard wake displacement also affects the aircraft directional stability. Results collected in this work have been useful to perform a redesign of the aircraft empennage and to schedule numerical high-fidelity analyses as well as a second wind tunnel test campaign on the updated aircraft model to get further insights on the aerodynamic interference, including propulsive effects

Improvement of Take-Off Performance for an Electric Commuter Aircraft Due to Distributed Electric Propulsion

The need for environmentally responsible solutions in aircraft technology is now considered the priority for global challenges related to the limited supply of traditional fuel sources and the potential global hazards associated with emissions produced by traditional aircraft propulsion systems. Several projects, including research into highly advanced subsonic aircraft concepts to drastically reduce energy or fuel usage, community noise, and emissions associated with aviation, are currently ongoing. One of the proposed propulsion concepts that address European environmental goals is distributed electric propulsion. This paper deals with the detailed aerodynamic analyses of a full-electric commuter aircraft with fuel cells, which expects two primary electric motors at the wing tip and eight other electric motors distributed along the wingspan as secondary power sources. The main objective was the numerical estimation of propulsive effects in terms of lift capabilities at take-off conditions to quantify the possible reduction of take-off field length. However, the aircraft was designed from scratch, and therefore a great effort was spent to design both propellers (for the tip and distributed electric motors) and the wing flap. In this respect, several numerical tests were performed to obtain one of the best possible flap positions. This research work estimated a reduction of about 14% of the take-off field length due to only the propulsive effects. A greater reduction of up to 27%, if compared to a reference conventional commuter aircraft, could be achieved thanks to a combined effect of distributed propulsion and a refined design of the Fowler flap. On the contrary, a significant increment of pitching moment was found due to distributed propulsion that may have a non-negligible impact on the aircraft stability, control, and trim drag

Computational simulation of the excited states dynamics of azobenzene in solution

Azobenzene and its derivatives are molecules very often used to construct photomodulable materials and molecular devices. The main characteristic of this kind of molecules is the efficient and reversible trans → cis photoisomerization, that occurs in either sense, without secondary processes. Using the appropriate wavelength, one can convert either isomer into the other one. The photoisomerization mechanism of azobenzene has been debated, during the last decades, because of the peculiar wavelength dependence of the quantum yields and because at least two standard possibilities exist: N=N double bond torsion and N inversion. Our research group has performed simulations of the photodynamics of azobenzene molecule by mixed quantum-classical methods. Such simulations have been successful in explaining the dependence of the quantum yield on the excitation wavelength. However, these simulations have been conducted on the isolated azobenzene molecule, while almost all the experimental data have been obtained in condensed phase. In particular, Diau's group, from Taiwan, has shown a strong dependence of the excited states dynamics on the solvent viscosity. The general aim of this work is to study the excited state dynamics of azobenzene in solution, in order to obtain its transient spectra and to produce data directly comparable with the experiments. In particular, we have studied the quantum yields, the isomerization mechanism and the reorientation of the transition dipole moment during the excited state relaxation, in order to understand the time resolved fluorescence anisotropy measurements obtained by Diau and collaborators. This research will also permit to study the reorientation of the whole molecule, which leads to alignment of an azobenzene sample in a polarized laser field. A basic issue for the interpretation of the fluorescence anisotropy and of the orientation of azobenzene samples in polarized light is related with the direction of the transition dipole vector for the forbidden n-π* transition of trans-azobenzene. Therefore, we have carried out a preliminary ab initio study of the n-π* transition dipole moment, considering the vibrational motions that contribute to the oscillator strength, and focusing on the most effective ones, i.e. those of lowest frequency. The most effective coordinate in promoting this transition is the symmetric torsion of the phenyl groups. Other important coordinates are the antisymmetric phenyl torsion and the torsion of the N=N double bond. The transition dipole vector turns out to lie essentially in the molecular plane, almost parallel to the N-C bonds and to the longest axis of the molecule. Semiempirical calculations are in sufficiently good agreement with those obtained by ab initio methods. The main part of the thesis work has been devoted to the simulation of the dynamics of the photoisomerization process of azobenzene in solution. We have made use of a mixed quantum-classical method of the surface hopping family. The electronic energies and wavefunctions are computed on the fly, by a semiempirical method modified by our group. A reparameterization of the semiempirical AM1 Hamiltonian has been carried out, considering new ab initio results used as reference values, in order to improve the accuracy of the semiempirical PES. The solvent effects have been introduced in a preliminary way by brownian dynamics, simulating two different solvent viscosities, and then explicitly, with a QM/MM approach. In this approach, the solvent itself is represented by a Molecular Mechanics force-field (OPLS) and the QM/MM interactions are made of electrostatic and Lennard-Jones terms. We have first determined, by ab initio calculations, the solute-solvent interaction potential between azobenzene and two simple molecules, methane and methanol (representatives of non-polar and of protic compounds). In this way we have obtained the necessary QM/MM interaction parameters, and we have run simulations with two solvents used in the experiments, methanol and ethylene glycol (simulations with n-hexane are in progress). We obtain very good results for the dependence of the quantum yields on the solvent viscosity, and in this way we can confirm that the photoisomerization mechanism is dominated by the torsion of the N=N double bond. The simulations also provide the necessary information to compute the time-resolved fluorescence spectra and anisotropy, i.e. for a complete reproduction of the experimental results. We have obtained a good agreement with the measured time-dependent intensities and anisotropies, but our explanation of the mechanism partly differs from that put forward in the experimental work