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To perform a reliable video analysis, it is mandatory to avoid shaking the camera while taking the video, normally using a tripod for smartphones/cameras. But there are some situations which the only chance to make the video is using your hands and it is almost impossible to avoid shaking the camera even trying your best. Imagine the following situation: a volleyball is obliquely launched, and the video is filmed by hand. Then, a point that is fixed in relation to the ground is chosen as the origin of a ground fixed reference frame. Despite being a ground fixed point, it will appear shaky in images captured by the handheld camera. Thereby, two standard video analyses are performed, one from the ground fixed point random shaking and one from the ball’s trajectory, both in relation to the default reference frame of the video analysis software. Lastly, to implement the video analysis of the relative ball movement it is enough to subtract the position coordinates of the ball’s movement by the position coordinates of the ground fixed point tremble, at each instant of time. The graphs of the position and velocity components versus time are presented, and the results are discussed. Em uma videoanálise confiável, evita-se balançar a câmera durante a filmagem, normalmente usando um tripé para smartphones/câmeras. Mas existem algumas situações em que a única chance de fazer o vídeo é usando as mãos e é quase impossível evitar balançar a câmera mesmo tentando o seu melhor. Imagine a seguinte situação: uma bola de vôlei é lançada obliquamente e o vídeo é filmado à mão. Em seguida, um ponto que é fixo em relação ao solo é escolhido como a origem de um referencial fixo do solo. Apesar de ser um ponto fixo no solo, ele aparecerá trêmulo nas imagens capturadas pela câmera. Desse modo, duas videoanálises padrão são realizadas, uma do tremor aleatório do ponto fixo no solo e outra da trajetória da bola, ambas em relação ao referencial padrão do software de análise de vídeo. Por fim, para implementar a videoanálise do movimento relativo da bola, basta subtrair suas coordenadas de posição pelas coordenadas de posição do ponto fixo do solo, a cada instante de tempo. Esta técnica reduz drasticamente o efeito de vibração nas variáveis cinemáticas. Os gráficos dos componentes de posição e velocidade em função do tempo são apresentados e os resultados são discutidos.

Nowadays, in almost any country in the world, it is difficult to find a young person who has never played with, seen, or heard of the most famous toy in 2017: the fidget spinner. According to Wikipedia: “The fidget spinner is a toy that consists of a ball-bearing in the center of a multi-lobed flat structure made from metal or plastic designed to spin along its axis with little effort.” Articles on educational proposals related to fidget spinners have been presented recently. Naturally, an issue arises from this polemic context: can fidget spinners be used to illustrate or explain physics concepts such as moment of inertia, torque, and angular momentum? This paper presents a simpler, cheaper, and easier experimental setup to obtain moments of inertia of the fidget spinner by using the free software Tracker for video analysis. A consistency test with an aluminum cylindrical shell ensures the reliability of the experimental setup.

Resumo O momento angular de um sistema de partículas e a sua divisão em um termo orbital e um termo de spin é um assunto normalmente relegado a segundo plano, ou mesmo ausente, nas disciplinas introdutórias de mecânica dos cursos de graduação. Além disso, a conservação do momento angular de um sistema, na ausência de torques externos, pode ser muitas vezes contraintuitiva. O presente trabalho se utiliza de um brinquedo chamado flat ball, que têm um formato semelhante a discos, no contexto de uma colisão bidimensional. Duas flat balls idênticas são lançadas girando em sentidos opostos e colidem, sobre uma superfície de atrito desprezível. O experimento tem grande potencial pedagógico porque proporciona uma análise qualitativa e quantitativa das grandezas momentos linear e angular do sistema, bem com a sua conservação, empregando a técnica de videoanálise. O resultado surpreendente do experimento tem o potencial de despertar a curiosidade dos estudantes, bem como abre o caminho para abordar a transição dos módulos do momento angular orbital e de spin do sistema, antes e depois da colisão.

This work address the preconceptions of first year engineering students about the kinematic graphs and the outcomes of a pedagogical strategy that relies on Predict – Observe – Explain learning method mediated by a video analysis software. The whole learning procedure was accompanied by a written material as students’ worksheets which enabled a formal record of the students’ conceptions throughout the process. The Test of Understanding of Kinematics Graphs was utilized to evaluate the students’ preconceptions and learning gains. It was found that first year engineering students had serious difficulties in drawing and interpreting kinematic graphs. Although interpretation of graphs and the understanding of the velocity and acceleration concepts improved, the preconceptions were quite resilient.

The drag effect on a falling ball caused by air is a conventional subject in the most well-known textbooks of classical mechanics and fluid dynamics. Further, there are some papers that employ video analysis to track objects movements in the air making it possible to obtain position data as a function of time and its graphs. However, none of them addresses the case of a ball thrown downwards, maybe because this situation is neglected by textbooks or probably due to the experimental difficulty to perform this kind of launch manually. In this paper, both the fall and the vertical launch down of five different Styrofoam balls are filmed with an ordinary smartphone camera and analysed by using the free software Tracker. The position and velocities graphs depicted clearly the air drag effect on the ball’s movements. The entire raw data are compared with a theoretical model and therefore terminal and initial velocities can be extracted as adjusted parameters from simple mathematical fits. The Reynolds number and the drag coefficient calculated for each ball agree with those found in the literature.

In general, undergraduate experimental physics laboratories do not usually have experiments designed to address rolling friction and to measure the value of the rolling friction coefficient. This work explores an experiment, which has the potential to arouse students’ curiosity about rolling friction by addressing a counterintuitive aspect of the behavior of a sphere that rolls up, stops and then rolls down on an inclined track. In fact, due to the difference in the net static friction in the upward and downward movements caused by the rolling friction term, the sphere’s acceleration when rolling upward is higher than when rolling downward. This difference, which had been predicted theoretically, was easily demonstrated graphically by video analysis, using both rubber and mouse balls. For two steel balls, this difference was more subtle, but it was still possible to detect it numerically. The experimental setup employed typical laboratory equipment and the free video analysis software Tracker to collect position and velocity data. The rolling friction coefficient was calculated with good precision by means of an angular coefficient of a fitted first-degree function involving appropriate variables.

Objective: To examine the impact of surgical margin width on survival following R0 hepatic resection for colorectal metastases (CRLM). Summary of Background Data: Although negative resection margin is considered of paramount importance for the prognosis of patients with colorectal liver metastases, optimal resection margin width remains controversial. Methods: Eligible studies examining the association between margin status after R0 hepatic resection for CRLM and survival, including overall survival (OS) and disease-free survival (DFS) were sought using the Medline, Cochrane, and EMBASE databases. Random-effects models were used for the calculation of pooled relative risks (RRs) with their 95% confidence intervals (95% CIs). Results: Thirty-four studies were deemed eligible for inclusion representing a cohort of 11,147 hepatic resections. Wider resection margin (>1 vs 1cm resection margin at 3, 5, and 10 years. Interestingly, >1mm (vs 1mm margin is associated with better prognosis than a submillimeter margin, achieving a margin >1cm may result in even better oncologic outcomes and should be considered if possible. Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.

This study was aimed for development of vapour-grown carbon nano-fibre(VGCNF)-reinforced aluminium matrix composites by the low-pressure infiltration process. First, VGCNF and Al powder (VGCNF + Alp) preforms for low-pressure infiltration were fabricated by spark sintering process at pressures of 5, 10, 20 and 40 MPa, respectively. Porosity of the preforms fabricated at pressures of 5 and 10 MPa was 44·89 and 40·87%, respectively. However, porosity of the preforms fabricated by spark sintering at pressures of 20 and 40 MPa was approximately 20%. Therefore, VGCNF + Alp/Al composites with the preform sintered at pressures of 5 and 10 MPa were fabricated by the low-pressure infiltration process under an applied pressure of 0·4 MPa, and the relative density was 81·4 and 76·0%, respectively. Moreover, the microstructure, porosity and electrical conductivity of the VGCNF + Alp/Al composites were estimated. Their electrical conductivities reduced with increasing porosity of VGCNF + Alp/Al composites.

Neste trabalho propomos e investigamos uma proposta didática para o ensino de espelhos esféricos baseada na associação entre uma metodologia de aprendizagem ativa com a estratégia de analogias ponte e conceitos âncora. A atividade era constituída por dois experimentos sucessivos sobre as características de imagens virtuais conjugadas por um espelho esférico côncavo e a dependência de seu tamanho relativo com a posição do observador (ângulo visual). O público-alvo era composto por quatro turmas distintas de ensino médio de uma escola da rede federal. Todo o procedimento foi acompanhado de um material escrito na forma de questionário. Para analisar qualitativamente os diferentes tipos de resposta e também a evolução dos estudantes foi utilizada a taxonomia de reações de Chinn e Brewer. Os resultados obtidos revelam as seguintes conclusões: (i) Ratifica a crítica presente na literatura que o emprego isolado do conflito cognitivo não conduz a mudanças significativas nos conceitos prévios da grande maioria dos alunos. (ii) A estratégia de associar uma metodologia de aprendizagem ativa que provoque o conflito cognitivo com as analogias ponte foi bem sucedida em viabilizar uma mudança da teoria da maioria dos alunos (iii) A necessidade de pesquisas quantitativas complementares para avaliar ganhos de aprendizagem. In this paper we propose and investigate a teaching proposal about convergent mirror based on the association between an active learning methodology and method of bridge analogies and anchorings concepts. The activity consisted of two successive experiments on the characteristics of virtual images formed by the concave spherical mirror and dependence on their relative size with the observer position (visual angle) were. Four high school distinct classes of the federal system of education formed the target audience. The whole procedure was accompanied by a written material as worksheets. To evaluate qualitatively their different types of reaction and also the evolution facing the anomalous data from the first experiment, we used the reactions taxonomy created by Chinn and Brewer was used. The results show the following conclusions: (i) it ratifies the present criticism in the literature that the isolated use of cognitive conflict does not lead to significant changes in the previous conceptions of most pupils; (ii) The strategy of associating an discrepant experiment causing cognitive conflict with another bridge experiment, of predictable result that rescue anchoring correlated ideas by analogy, has been successful in achieving a theory change in the most of students; (iii) The need for further quantitative research to evaluate learning gains.

Em geral, os artigos na área de ensino sobre propagação de pulsos ou de ondas estacionárias utilizam fios ou arames muito leves, cujos pesos são desprezíveis diante das tensões aplicadas. Essa aproximação simplifica tanto a equação de onda, tornando-a linear, como a relação entre a tensão e a velocidade da onda. Entretanto, esse procedimento restringe os experimentos e exige o uso de sensores e/ou equipamentos mais caros para extrair dados confiáveis. Diferentemente, o objetivo deste trabalho foi criar e analisar um experimento didático barato e eficiente para a obtenção da relação entre a velocidade e a tensão de um pulso e da densidade linear de uma corda, cuja massa não fosse desprezível. Nessa situação, a corda não fica em linha reta, mas pende devido ao seu próprio peso formando uma curva chamada catenária. Para a coleta de dados, foram empregados somente uma câmera de filmagem de um smartphone e um software gratuito de videoanálise. Os diferentes modelos teóricos aplicados na interpretação dos resultados permitiram uma compreensão mais ampla e profunda do experimento. A análise dos resultados revelou uma variação da acurácia e precisão de acordo com os modelos matemáticos adotados. Isso possibilitou uma interessante visualização de que o trabalho experimental não depende somente dos equipamentos empregados, mas é indissociavelmente entrelaçado com as respectivas teorias. Além disso, as diferentes formas de modelar um mesmo fenômeno, com uma gradação de complexidade, proporcionam abordagens ajustadas para os níveis médio e superior, bem como para os diversos cursos de graduação. In general, the articles in the teaching area on pulses propagation or standing waves use very light wires or whose weights are negligible compared to the applied tensions. This approach both simplifies the wave equation making it linear as the relationship between the tension and the speed of the wave. However, this procedure restricts the experiments and requires the use of sensors and/or more expensive equipments to extract reliable data. In contrast, the aim of this work was to create and analyze a cheap and efficient educational experiment to obtain the relationship between the speed and the tension of a pulse and the linear density of a rope, whose mass was not negligible. In this situation, the rope is not straight, but hangs due to its own weight forming a curve called catenary. For data collection were employed only a camera of a smartphone and a free video analysis software. Different theoretical models applied in interpreting the results enabled a wide and deeper understanding of the experiment. The results showed a variation in the accuracy and precision according to the mathematical models adopted. This provided an interesting view, that is, the experimental work depends not only on the equipment used, but is entangled with the respective theories. Also, the different ways of modeling the same phenomenon, with a gradation of complexity, provide approaches adjusted to the high school and superior levels as well as for the various undergraduate courses.

A nonlinear vector supersymmetry for three-dimensional topological massive Yang-Mills is obtained by making use of a nonlinear but local and covariant redefinition of the gauge field., 8 pages, LateX2e

Currently, the number of smartphones with an embedded gyroscope sensor has been increasing due games whose performance relies on 3D augmented reality. In general, teaching papers on the gyroscope sensor address very simple spatial configuration, where the fixed rotation axis coincides to the z-axis of the smartphone. This work presents five experimental setups with different spatial orientations of a smartphone on a turntable. The total angular velocity vector of the turntable is constant, but its projections on the three fixed Cartesian axes of the smartphone varies for the five spatial orientations investigated. For the sake of consistency, the magnitude of the vector sum of the three angular velocities components yielded by the gyroscope sensor was checked by video analysis using the free software, Tracker. The internal consistency between the results provided by this video analysis technique and data from the gyroscope assures us this sensor is reliable for teaching proposals. The main goals of this paper are (i) encourage teachers to effectively incorporate the gyroscope sensor of smartphones in to their classrooms, especially in high schools and undergraduate physics and engineering courses; (ii) spread in the academic syllabus the Tait–Bryan convention, a very intuitive way to perform 3D rotations and; (iii) explain how to interpret data of the three components of angular velocity obtained by the gyroscope sensor in different spatial orientations.

In the present work, we develop a low-cost and simple experiment to visualise Fourier's synthesis using a short, soft, and light plastic coiled spring oscillating in a horizontal plane, and a basic camera (120 fps). It is shown that the spring obeys a linear wave differential equation, as gravitational influence is neglected. A nonlinear criterion is evaluated to determine if magnitudes of the parameters in the initial conditions satisfy the linear wave equation. Our setup promotes some desirable characteristics that make Fourier's synthesis experiments feasible, visual, and enlightening: (i) it requires few, common, and cheap resources, and the experiment can be carried out even in a high-school laboratory; (ii) since the spring's tension is small (~1 N, on average), the frequencies of normal modes are low (close to 2 Hz), and therefore, it is possible to record the oscillations just with the camera and extract a considerable number of position and time data in just one cycle; (iii) when the video is loaded in the Tracker free software, it can be reproduced in slow motion. Since the frequencies involved are low, an interesting and instructive temporal sequence of images of the spring displaying the typical trapezoidal shape appears clearly; (iv) the tools associated with the Tracker software tools can yield the relevant oscillation parameters, such as the damping constant, amplitudes, frequencies, and phases; and (v) it is possible to carry out superposition of a snapshot of the spring in Tracker at any time, and to draw the related Fourier synthesis graphs. The visual match between the shape of the spring and the theoretical graph is remarkable, and can be enhanced by adding the damping term.

Os roteiros e livros que servem de guias para o ensino de Mecânica nos laboratorios didaticos de fisica experimental no ensino superior costumam apresentar uma experiencia que consiste em abandonar uma esfera metalica do topo de uma plataforma de lancamento curva suspensa por um suporte apoiado sobre uma bancada. Ao alcancar a base da plataforma, a esfera e lancada horizontalmente deixando marcado o seu alcance em uma folha com o auxilio do papel carbono. Essa experiencia serve para ilustrar a conservacao da energia mecânica, supondo a hipotese de que a esfera execute um rolamento puro, bem como mostrar a importância de levar em conta a sua energia cinetica de rotacao. Contudo, na forma como o experimento e tradicionalmente apresentado nao ha uma descricao em tempo real do movimento e por isso nao e possivel perceber que a esfera desliza e rola na maior parte do percurso, so alcancando a condicao de rolamento puro ao final da plataforma. Esse equivoco no tratamento e o motivo da sistematica diferenca entre o balanco de energia previsto e aquele obtido pelas medidas experimentais. Neste trabalho, desenvolvemos um modelo teorico que considera tanto a curvatura da plataforma como os efeitos de borda devido ao encaixe parcial da esfera na largura da calha. Atraves da videoanalise extraimos dados experimentais do movimento completo que ilustram claramente uma transicao do rolamento com deslizamento para o rolamento puro para diferentes ângulos de inclinacao inicial analisados, bem como obtemos o valor aproximado do tempo de transicao para um dos casos.

We report on the use of butterfly-type fiber-Bragg-grating external cavity semiconductor laser (FGL) modules in dense wavelength-division multiplexing (DWDM) applications. In a dense wavelength-multiplexing experiment, we demonstrated that successive four-channel multiplexing with 25-GHz spacing and with almost the same peak power was realized by using the FGLs. The lasing wavelength of each channel was tuned to the corresponding wavelength grids with an accuracy of /spl plusmn/1 pm. In the DWDM transmission with 25-GHz channel spacing and 2.5-Gb/s direct modulation using a standard single mode fiber (SMF), a good bit-error ratio (BER) performance without floor phenomenon was achieved up to 300 km. There was no degradation of transmission characteristics caused by the optical crosstalk from adjacent channel. Even in the DWDM transmission where channel spacing was 12.5 GHz, good transmission characteristics were maintained up to 300 km and little degradation of BER performance occurred at 300 km compared with the single-channel transmission. In addition, we investigated the influence of external temperature change on the FGL reliability using temperature-cycling test. As a result, we clarified that the characteristic degradation of FGL after this test was sufficiently small and that this device had a high tolerance to the severe external temperature variation.

Oxygen diffused into silicon from a sodium-depleted region during Si/glass anodic bonding. The diffusion formed amorphous silicon oxide that accounted for the bond formation. Ion migrations within the sodium-depleted region were complicated.

We study and explore the symmetry properties of fermions coupled to dynamical torsion and electromagnetic fields. The stability of the theory upon radiative corrections as well as the presence of anomalies are investigated., Comment: 9 pages, LaTex

The interfacial microstructure of anodic-bonded Al/glass was investigated to obtain a better understanding of the bonding process. The experimental results demonstrate that a sodium-depleted region existed in the glass adjacent to the aluminum. Aluminum diffused into the glass for about 500 nm when the Al/glass was anodic-bonded at 250 °C, 700 V and 420 s. Furthermore, a crystalline region about 10 nm thick developed in this aluminum-diffused region of the glass. The crystalline region was greatly aluminum-diffused. No aluminum oxide region existed at the interface. It is therefore concluded that the diffusion of aluminum into the glass is responsible for bond formation. This conclusion does not agree with the conventional anode oxidation model based on the assumption that aluminum does not diffuse into the glass.

Os laboratórios didáticos de física experimental, tanto no ensino médio quanto no ensino superior, não costumam abordar experimentos didáticos que contemplem a medida do coeficiente de atrito de rolamento. Aliás, o próprio conceito de atrito de rolamento é sistematicamente ignorado nas coleções de ensino médio e até mesmo naquelas de ensino superior. Neste artigo propomos um experimento de baixo custo usando apenas uma pilha média comum, uma câmera de smartphone e o software livre Tracker para vídeo-análise. Além disso, integramos em uma só experiência didática a medida de duas grandezas físicas distintas, a saber, o coeficiente de atrito cinético e o coeficiente de atrito de rolamento. De fato, a vídeo-análise do movimento completo da pilha, lançada manualmente sobre uma superfície horizontal plana, permite dividir o movimento em duas partes: rolamento com deslizamento seguido de rolamento sem deslizamento. O software Tracker provou ser uma ferramenta eficiente para a obtenção de medidas de posição do centro de massa e de tempo, nas duas fases do movimento. Com esses resultados foram calculados diversos parâmetros da teoria, em especial os dois coeficientes de atrito, com bastante acurácia e precisão. The teaching laboratories of experimental physics, both at high school and at undergraduate level, do not usually address didactic experiments that include the measurement of the rolling friction coefficient. Indeed, the concept of rolling friction is systematically ignored in the collections of high school and even those of university education. In this paper we propose a low cost experiment using just an ordinary cylindrical battery, a smartphone camera and the free software Tracker for video analysis. Moreover, integrated into one didactical experience, one can measure two distinct physical quantities, namely kinetic and rolling friction coefficients. In fact, the video-analysis of the complete cylindrical battery movement, launched manually on a flat horizontal surface, allows splitting the movement in two parts: rolling with slip followed by rolling without slipping. The Tracker software has proven to be an efficient tool for obtaining measurements of the center of mass position and time in both phases of the movement. The experimental results allow very accurate and precise calculations of various theoretical parameters, in particular the two friction coefficients.

The vector supersymmetry of the two-dimensional (2D) topological BF model is extended to 2D Yang-Mills. The consequences of the corresponding Ward identity on the ultraviolet behaviour of the theory are analysed.

Insert casting of aluminum is widely used in industry. In order to realize better metallurgical bonding between metallic pipe and aluminum alloy castings, a new insert casting method with aided by high-power ultrasound has been developed. The bonding strength between the metal pipe and the cast aluminum alloy was evaluated by shear testing, EPMA analysis at the bonding interface was performed. The experimental results indicate that the application of ultrasonic vibration was effective during insert casting, particularly immediately after the primary a phase began to emerge in the cast aluminum melt. In the case of 6061 Al pipe/AC4C joint, the shear strength was approximately 60 times higher than without ultrasound vibration. This bonding reflects the break up of the oxide film on the aluminum pipe surface by the ultrasound cavitation effect. For the steel pipe/AC4C joint, the bonding shear strength had a several-fold enhancement. Ultrasound may promote a chemical reaction between steel and cast a...

We study the effect of a finite temperature on the correlation function of quantum magnetic vortex lines in the framework of the (3 + 1)-dimensional Abelian Higgs model. The vortex energy is inferred from the large distance behavior of these correlation functions. For large straight vortices of length L, we obtain that the energy is proportional to TL2 differently from the zero temperature result which is proportional to L. The case of closed strings is also analyzed. For T = 0, we evaluate the correlation function and energy of a large ring. Finite closed vortices do not exist as genuine excitations for any temperature.

Aluminium alloy 6061, AC8A, Al–1Mg, Al–9Cu and pure aluminium composites reinforced with aluminium borate whiskers were fabricated by a squeeze casting process. The interfacial reaction in the composites and its effect on the bending strength are discussed, together with the results from SEM, TEM, and X-ray diffraction. A slight interfacial reaction is favourable for composite strength as it has the effect of anchoring the whiskers. A T6 treatment can enhance the strength of an Al–9Cu matrix composite, but is not efficient for magnesium containing 6061 and AC8A matrix composites. Furthermore, if heated at temperatures higher than 793 K for a long time, the composite strength drops rapidly owing to whisker damage and shortening during the interfacial reaction. It is suggested that the interface in an Al18 B4O33 /Al alloy composite is stable below 623 K which is the temperature requirement for automobile engine components.

The supersymmetric descent equations in superspace are discussed by means of the introduction of two operators which allow to decompose the supersymmetric covariant derivatives as BRS commutators.

The existence of the vector supersymmetry for three dimensional cohomological field theories is discussed. The example of the three dimensional topological model of Baulieu-Grossman [1] is considered in detail.

Classical three dimensional Yang-Mills is seen to be related to the topological Chern-Simons term through a nonlinear but fully local and covariant gauge field redefinition. A classical recursive cohomological argument is provided., Comment: 8 pages, LateX2e file

Sapphire (α–Al2O3) and Al were joined by means of the surface activated bonding (SAB) method in an ultrahigh vacuum at room temperature. Tensile tests have shown that failure occurred not along the interface but inside the Al bulk near the interface. High resolution transmission electron microscopy has revealed the formation of a direct interface between Al and sapphire, indicating the possibility to artificially fabricate an atomically direct interface of dissimilar materials at room temperature. However, an intermediate layer was partially observed, which might be attributed to the effect of fast atom beam irradiation of the sapphire surface.

Os livros didáticos de física utilizam a definição do aumento linear transversal (AL) com o objetivo de comparar o tamanho da imagem ao do objeto quando abordam espelhos e lentes esféricas. Este trabalho discute as distorções geradas pela utilização do conceito de AL e emprega o conceito de aumento angular (AA) para demonstrar que a visão do observador acerca do tamanho relativo entre o objeto e a sua imagem associada produzida por um espelho esférico côncavo depende da sua própria posição. Foi realizada uma análise qualitativa de dois experimentos, e ainda análises quantitativas e gráficas da variação do módulo do AA em função da posição do observador para os quatro tipos de imagens produzidas por um espelho côncavo. Discute-se a necessidade da introdução do conceito de aumento angular nos livros didáticos para compreender a visualização das imagens formadas por um espelho esférico côncavo. The physics textbooks use the definition of linear magnification (LM) in order to compare the size of the image with the object when addressing spherical mirrors and lenses. This work discusses the distortions generated by using the concept of LM and employs the angular magnification (AM) to show that the vision of the observer about to the relative size between the object and its associated image produced by concave spherical mirror depends on its own position. It was performed a qualitative analysis of two experiments, and even quantitative and graphics analysis of the modulus variation of AA as a function of the observer position for four types of images produced by a concave mirror. It is discussed the need of the introduction of the angular magnification concept in textbooks to understand the visualization of images formed by a concave spherical mirror.

We present here the zero curvature formulation for a wide class of field theory models. This formalism, which relies on the existence of an operator $\d$ which decomposes the exterior space-time derivative as a BRS commutator, turns out to be particularly useful in order to solve the Wess-Zumino consistency condition. The examples of the topological theories and of the $B$-$C$ string ghost system are considered in detail.

In the predominant approach in physics textbooks, the collision between particles is treated as a black box, where no physical quantity can be measured. This approach becomes even more evident in experimental classes where collisions are the simplest and most common way of applying the theorem of conservation of linear momentum in the asymptotic behavior. In this paper we develop and analyse an experiment on collisions using only two smartphones. The experimental setup is amazingly simple; the two devices are aligned on a horizontal table of lacquered wood, in order to slide more easily. At the edge of one of them a piece of common sponge is glued using double-sided tape. By using a free smartphone application, the values generated by the accelerometer of the two devices in full motion are measured and tabulated. Through numerical iteration, the speed graphs of the smartphones before, during, and after the collision are obtained. The main conclusions were: (i) the demonstration of the feasibility of using smartphones as an alternative to air tracks and electronic sensors employed in a teaching lab, (ii) the possibility of investigating the collision itself, its characteristics and effects; this is the great advantage of the use of smartphones over traditional experiments, (iii) the compatibility of the results with the impulse-momentum theorem, within the margin of uncertainty.

As a low-cost light source for wavelength-division-multiplexing networks, the authors develop an uncooled coaxial fiber Bragg grating external-cavity semiconductor laser (FGL). To realize high-wavelength stability, an FGL structure is adopted, and to reduce the cost of light source itself, a coaxial pigtail module structure is selected. High-wavelength stabilities of 2 pm/mA and 12 pm/K against current and ambient temperature variation are realized. Using the FGLs, successive eight-channel wavelength multiplexing with 200-GHz spacing and with almost the same peak power is realized between -30/spl deg/C to 70/spl deg/C. For each channel, the wavelength difference from the corresponding ITU grid is only within /spl plusmn/0.1 nm at 25/spl deg/C.

The successful fabrication of an eight-channel optoelectronic integrated receiver array on an InP substrate, which comprises eighty elements including GaInAs p-i-n photodiodes (PDs) and AlInAs/GaInAs HEMTs, is reported. An average bandwidth of 1.2 GHz with a standard deviation of 190 MHz over the whole channel was obtained. An average responsivity was 546 V/W with a standard deviation of only 19.2 V/W. A crosstalk was less than -30 dB at frequencies between 3 and 900 MHz and as small as -28 dB even at 1 GHz. The yield of chips available for 1.0 Gb/s operation was as high as 62.5% over 2-in-diameter wafer. >

An ultra-high-speed optoelectronic integrated receiver consisting of a GaInAs p-i-n photodiode and a transimpedance AlInAs-GaInAs high-electron-mobility-transistor amplifier was successfully fabricated on an InP substrate. A 3-dB bandwidth of 6 GHz with a transimpedance of 50 dB Omega was achieved for the receiver with a feedback resistance of 750 Omega . Measured noise currents of the receiver were analyzed and found to be dominated by the low-frequency noise and the induced gate noise. A sensitivity of -21.2 dBm for 8.0-Gb/s NRZ signals was deduced from the noise current characteristics. >

Motivated by the interest raised by the problem of Lorenz-symmetry violating gauge theories in connection with gravity models, this contribution sets out to provide a general method to systematically study the excitation spectrum of gravity actions which include a Lorentz-symmetry breaking Chern–Simons-type action term for the spin connection. A complete set of spin-type operators is found which accounts for the (Lorentz) violation parameter to all orders and graviton propagators are worked out in a number of different situations.

An artificially formed Σ = 13(67.38°)[100] tilt boundary in an Ni3(Al0.6 Ti0.4) crystal was investigated with end-on view by high resolution transmission electron microscopy. The result indicates that the atomic arrangement at the boundary was symmetric without any appreciable lattice distortion around it, and multislice calculations based on the coincidence site lattice model interpreted well the observed TEM images. Brief discussions were given in comparison with other geometrical models of the grain boundary.

A 10-bit analog-to-digital converter applicable to digital video equipment and using 0.8- mu m BiCMOS technology is discussed. In order to reduce power dissipation and chip size, a two-step parallel type conversion scheme is utilized. The 10-bit resolution has been realized at a maximum conversion rate of 40 MHz, power dissipation of 700 mW, and chip size of 4.1*4.8-mm/sup 2/. A scheme that transforms coarse reference voltages to fine ladder resistors using buffer amplifiers has been used. As the emitter follower circuit can be used for the buffer amplifier, a small settling time is obtained. A subranging architecture has been adopted in which the full-scale range of fine ADC is consistent with the equivalent voltage to 1.5 LSB for coarse ADC. With this architecture, 10 bit resolution is not required for coarse ADC, and total resolution is decided by fine ADC. >

The effect of the interfacial native oxide layer between polycrystalline and single-crystal Si was investigated in the submicron-rule bipolar and BiCMOS processes. It was found that the native oxide increases the current gain, but significantly degrades bipolar transistor performance. Bipolar transistors without the oxide layer, fabricated by different methods, were investigated. Without the layer, low emitter resistance and small current gain variation were achieved for a low-temperature process. The current gain reduction due to the lack of the oxide layer does not degrade the cutoff frequency. Improved performance for structures without native oxide was confirmed with ECL (emitter-coupled logic) ring oscillators. >