Biblioteca Digital

Nesta pesquisa, estudamos como se desenvolve o processo argumentativo dos alunos sobre o conceito de fóton e se os estudantes se apropriam das interpretações da Mecânica Quântica para a natureza e o comportamento da luz. Para alcançar nossos objetivos, fizemos uma revisão da literatura sobre a importância da inserção de tópicos de Física Moderna e Contemporânea na escola média, das abordagens da Mecânica Quântica quanto à natureza e comportamento da luz, e das bases teóricas que alicerçam a análise da argumentação em sala de aula. A partir dessa revisão, foi possível perceber que o discurso dos estudantes é um fator de verificação de sua apropriação de conceitos. A análise das falas dos alunos ratificou essa constatação. Transcrevemos as falas e os gestos de quatro de onze aulas de uma sequência de ensino que objetivava investigar a natureza e o comportamento da luz em um interferômetro real e em uma extrapolação para o ideal, utilizando o arranjo experimental de Mach-Zehnder e um programa de computador que simula esse experimento. As gravações foram feitas em duas turmas do terceiro ano do ensino médio de uma escola pública. Para responder às questões de pesquisa propostas, analisamos as aulas que sistematizavam as discussões e os registros escritos finais dos alunos. A partir dos dados...

Chamamos caixa preta um conceito ou instrumento cujos detalhes de funcionamento e debates históricos (a seu respeito) são abandonados quando do seu uso. Um computador é um exemplo de objeto que é usado, em geral, sem que haja preocupação ou conhecimento com relação às nuances de seu funcionamento. O fato, já bem aceito, de que a fórmula química da água é H2O é outro exemplo de caixa preta, na medida em que alguém que afirma isso não precisa se preocupar em citar fontes ou remeter a discussões sobre a história da Química. Trabalhamos com a hipótese de que a ciência tornou-se, por si mesma, uma caixa preta. A forma como se evoca a autoridade do conhecimento científico nos meios de divulgação, em livros, diálogos e anúncios comerciais (onde frequentemente figuram fórmulas como "eficácia cientificamente comprovada") atesta um cenário atual onde a natureza da ciência e, em particular, a "comprovação" científica revelam algo que, estando carregado de poder, vem sendo veiculado, mesmo por cientistas, de maneira ingênua - sem passar por uma elaboração maior ou ignorando-se toda a complexa discussão, sobre esse assunto, presente na filosofia da ciência. Em nosso ensaio, discutiremos essa problemática...

This work presents new ab initio approaches to materials physics. We first introduce the multiscale approach to determination of thermal properties and changes in free energy. With this approach one can perform thermal averaging of ensembles of states with ab initio methods, thus enabling ab initio calculations of free energy changes. We use this method to perform an ab initio calculation of the free energy of reconstruction in the 300 reconstruction of silicon. In the next chapters we introduce a completely new approach to electronic structure calculations, using a new, real-space bais set (wavelets) which enables all-electron calculations of complex systems. By eliminating the need for pseudopotentials for decsribing the core, one can for the first time access the true density functional energy of a system through systematic convergence. In the final chapter we combine this method with the generalized gradient approximation to perform calculations on high-pressure phases of boron.; by Torkel D. Engeness.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2003.; Includes bibliographical references (leaves 157-162).

(cont.) is dictated by the solvent accessibility of structures. The distinct intrinsic tendencies of sequence and structure profiles are most pronounced at long periods, where sequence hydrophobicity fluctuates less, while solvent accessibility fluctuates more than average. Correlations between the two profiles can be interpreted as the Boltzmann weight of the solvation energy at room temperature. Chapter 4 shows that correlations in solvent accessibility along protein structures play a key role in the designability phenomenon, for both lattice and natural proteins. Without such correlations, as predicted by the Random Energy Model (REM), all structures will have almost equal values of designability. By using a toy, Ising-based model, we show that changing the correlations moves between a regime with no designability and a regime exhibiting the designability phenomenon, where a few highly designable structures emerge. Understanding how gene expression is regulated is one of the main goals of molecular cell biology. To reach this goal, the recognition and identification of DNA motifs--short patterns in biological sequences--is essential. Common examples of motifs include transcription factor binding sites in promoter regions of co-regulated genes and exonic and intronic splicing enhancers ...; In the past decade...

Contrary to classical physics, which was strongly objective i.e. could be interpreted as a description of mind-independent reality, standard quantum mechanics (SQM) is only weakly objective, that is to say, its statements, though intersubjectively valid, still merely refer to operations of the mind. Essentially, in fact, they are predictive of observations. On the view that SQM is universal conventional realism is thereby refuted. It is shown however that this does not rule out a broader form of realism, called here 'open realism', restoring the notion of mind-independent reality.; Comment: final version accepted in Found. Phys. (2 slight changes with respect to the former submission)

The panic stampede is a serious concern during mass events like soccer championship games. Despite huge numbers of security forces and crowd control measures, hundreds of lives are lost in crowd disasters each year. An analysis of video recordings of the annual pilgrimage in Makkah reveals how high-density crowds develop to turbulent dynamics and earthquake-like eruptions, which is impossible to control.; Comment: For a more detailed study see http://arxiv.org/abs/physics/0701203

English Language Learners (ELLs) are frequently left on the periphery of classroom interactions. Due to misalignment of language skills, teachers and peers communicate with these students less often, decreasing the number of opportunities to engage. Exclusion can be avoided with learning activities that invite all students to participate and contribute ideas. We argue that environments and activities that privilege scientific inductive reasoning increase possibilities for emerging bilingual students to engage. This study investigated first-grade students' discussions about factors that affect how objects float. Students came from a variety of language backgrounds; all were considered beginner/intermediate ELLs. Results show that the goal of inducing principles from actual phenomena encouraged students to communicate their ideas and reasoning, boosting students' confidence in expressing themselves. Following the hybrid space argument of Vygotsky's theory of concept formation, we illustrate that physics can be particularly suitable context for the co-development of concepts and English language skills.; Comment: 4 Pages; Physics Education Research Conference Proceedings - 2013, Portland OR

Students in inquiry science classrooms face an essential tension between sharing new ideas and critically evaluating those ideas. Both sides of this tension pose affective risks that can discourage further discussion, such as the embarrassment of having an idea rejected. This paper presents a close discourse analysis of three groups of undergraduate physics students in their first discussions of the semester, detailing how they navigate these tensions to create a safe space to make sense of physics together. A central finding is that students and instructors alike rely on a common discursive resource, epistemic distancing, to protect affect while beginning to engage with ideas in productive ways. The groups differ in how soon, how often, and how deeply they engage in figuring out mechanisms together, and these differences can be explained, in part, by differences in how they epistemically distance themselves from their claims. Implications for research include the importance of considering the coupled dynamics of epistemology and affect in collaborative sensemaking discussions. Implications for instruction include novel ways of encouraging classroom discussion.; Comment: 29 pages, 10 figures

We introduce an explicit solution for the non-equilibrium steady state (NESS) of a ring that is coupled to a thermal bath, and is driven by an external hot source with log-wide distribution of couplings. Having time scales that stretch over several decades is similar to glassy systems. Consequently there is a wide range of driving intensities where the NESS is like that of a random walker in a biased Brownian landscape. We investigate the resulting statistics of the induced current $I$. For a single ring we discuss how $sign(I)$ fluctuates as the intensity of the driving is increased, while for an ensemble of rings we highlight the fingerprints of Sinai physics on the $abs(I)$ distribution.; Comment: 9 pages, 8 figures, proofed published version

We show a new semi-quantitative technique of analysis about of temporal evolution of learning of basic physics concepts. In this technique we arrange a geometric diagram with the score and the homogeneity (H-S), in this diagram we have a quantitative and qualitative information about the learning of students and the effectiveness instruction. We applied this technique to study the temporal evolution of the graphical interpretation of motion in one dimension through tutorials in a introductory course physics with 20 students of engineering at the Universidad Central de Bogot\'a Colombia for a period of 6 weeks. We found in the general diagram that (Smax,Hmax)=(0.75,0.75).; Comment: 8 pages,6 figures. Submitted to Revista Brasileira de Ensino de F\'iisica

During last years poker has gained a lot of prestige in several countries and, beyond to be one of the most famous card games, it represents a modern challenge for scientists belonging to different communities, spanning from artificial intelligence to physics and from psychology to mathematics. Unlike games like chess, the task of classifying the nature of poker (i.e., as 'skill game' or gambling) seems really hard and it also constitutes a current problem, whose solution has several implications. In general, gambling offers equal winning probabilities both to rational players (i.e., those that use a strategy) and to irrational ones (i.e., those without a strategy). Therefore, in order to uncover the nature of poker, a viable way is comparing performances of rational versus irrational players during a series of challenges. Recently, a work on this topic revealed that rationality is a fundamental ingredient to succeed in poker tournaments. In this study we analyze a simple model of poker challenges by a statistical physics approach, with the aim to uncover the nature of this game. As main result we found that, under particular conditions, few irrational players can turn poker into gambling. Therefore, although rationality is a key ingredient to succeed in poker...

Network theory has unveiled the underlying structure of complex systems such as the Internet or the biological networks in the cell. It has identified universal properties of complex networks, and the interplay between their structure and dynamics. After almost twenty years of the field, new challenges lie ahead. These challenges concern the multilayer structure of most of the networks, the formulation of a network geometry and topology, and the development of a quantum theory of networks. Making progress on these aspects of network theory can open new venues to address interdisciplinary and physics challenges including progress on brain dynamics, new insights into quantum technologies, and quantum gravity.; Comment: (7 pages, 4 figures)

Problem Roulette (PR) is a web-based study service at the University of Michigan that offers random-within-topic access to a large library of past exam problems in introductory physics courses. Built on public-private cloud computing infrastructure, PR served nearly 1000 students during Fall 2012 term, delivering more than 60,000 problem pages. The service complements that of commercial publishing houses by offering problems authored by local professors. We describe the service architecture, including reporting and analytical capabilities, and present an initial evaluation of the impact of its use. Among roughly 500 students studying electromagnetism, we find that the 229 students who worked fifty or more problems over the term outperformed their complement by 0.40 grade points (on a 4.0 scale). This improvement partly reflects a selection bias that better students used the service more frequently. Adjusting for this selection bias by using overall grade point average (GPA) as a classifier, we find a grade point improvement of 0.22 for regular PR users, significantly above the random noise level of 0.04. Simply put, students who worked one or more additional problem per weekday earned nearly a quarter-letter average grade improvement irrespective of GPA. Student comments emphasize the importance of randomness in helping them synthesize concepts. The PR source code is publicly available on the bitbucket repository.; Comment: 22 pages...

We show that nonlinear dynamics in diode lasers with optical injection leads to frequency tunable microwave sidebands which are suitable for atomic physics experiments. We demonstrate the applicability of the sidebands in an experiment where rubidium atoms are magneto-optically trapped with both the trap and the re-pump optical frequencies derived from one optically injected laser. We find linewidth narrowing in the optical spectrum of the injected laser at both the injection frequency and the sideband frequency. With strong optical injection which leads to frequency locking we find a complete linewidth transfer from the master to the slave. Further applications are discussed.; Comment: 6 pages, 4 figures

Very little is known about how the nature of expertise in introductory and advanced courses compares in knowledge-rich domains such as physics. We develop a framework to compare the similarities and differences between learning and patterns of student difficulties in introductory physics and quantum mechanics. Based upon our framework, we argue that the qualitative patterns of student reasoning difficulties in introductory physics bear a striking resemblance to those found for upper-level quantum mechanics. The framework can guide the design of teaching and learning tools.; Comment: arXiv admin note: substantial text overlap with arXiv:1504.02042

In their study of physics beyond the first year of University -- termed upper-division in the US, many of students' primary learning opportunities come from working long, complex back-of-the-book style problems, and from trying to develop an understanding of the underlying physics through solving such problems. Some of the research at the upper-division focuses on how students use mathematics in these problems, and what challenges students encounter along the way. There are a number of different and diverse research studies on students' use of mathematics in the upper-division. These typically utilize one of two broad approaches, with some researchers primarily seeking out and addressing challenges students face, and others working chiefly to unpack students' in-the-moment reasoning. In this paper, we present and discuss both approaches, and then review research efforts that strive to connect these two approaches in order to make sense of students' use of mathematics as well as to uncover particular challenges that students encounter. These recent efforts represent a small step towards synthesizing the two approaches, which we argue is necessary to more meaningfully impact student learning at the upper-division. We close our review and discussion with suggested refinements for future research questions for the physics education research community to consider while it works to understand how students use math in upper-division courses.; Comment: 28 pages...

Most introductory quantum physics instructors would agree that transitioning students from classical to quantum thinking is an important learning goal, but may disagree on whether or how this can be accomplished. Although (and perhaps because) physicists have long debated the physical interpretation of quantum theory, many instructors choose to avoid emphasizing interpretive themes; or they discuss the views of scientists in their classrooms, but do not adequately attend to student interpretations. In this synthesis and extension of prior work, we demonstrate: (1) instructors vary in their approaches to teaching interpretive themes; (2) different instructional approaches have differential impacts on student thinking; and (3) when student interpretations go unattended, they often develop their own (sometimes scientifically undesirable) views. We introduce here a new modern physics curriculum that explicitly attends to student interpretations, and provide evidence-based arguments that doing so helps them to develop more consistent interpretations of quantum phenomena, more sophisticated views of uncertainty, and greater interest in quantum physics.; Comment: 14 pages, 11 figures; submitted to PRST-PER: Focused Collection on Upper-Division PER. arXiv admin note: text overlap with arXiv:1409.8499

Spacecraft neutralisers are required as part of the ion propulsion system for accurate station keeping in fundamental physics missions. This paper describes the use of thin layers of insulating materials as coatings for the gated silicon field emitter array structure used in a spacecraft neutraliser. These thin coatings are postulated to reduce power consumption and reduce overheating. The power consumption and lifetime of aluminium nitride and amorphous hydrogenated diamond-like carbon coatings have been tested by current-voltage and endurance tests. Diamond-like carbon coatings were promising, performing better in endurance tests than uncoated samples, but further work is required to characterise the coating's physical properties and its effects on field emission. The thermal conductivity of the coating material had little effect on measured sample lifetimes. Aluminium nitride had reduced power consumption compared to diamond-like carbon coated and uncoated samples. A thin (~5 nm) layer of aluminium nitride was found to be optimal, meeting European Space Agency specifications for the neutraliser engineering model.; Comment: Presented as a poster at 2004 COSPAR conference and submitted to Advances in Space Research. Horribly lost in their system for 7 years!

An account is presented of the special session on "Gender and Sexual Diversity Issues in Physics" which took place at the American Physical Society March Meeting 2012. The opinions of those who attended this session were solicited via an anonymous survey, the results of which are reported here. Drawing both upon ideas put forward by the speakers and audience from the meeting, a set of recommended actions is proposed for the Physics community to become more inclusive of LGBT+ people.; Comment: 10 figures, report of the session on "Gender and Sexual Diversity Issues in Physics" at the American Physical Society March Meeting 2012

The present paper aims to investigate parameters to evaluate the literary production on History and Philosophy of Science (HPS) directed to teaching and divulgation of Physics ideas through positive and negative aspects showed by authors of schoolbook reviews, paradidactic, scientific publishing, articles/essays focusing on HPS. These reviews are published in national literature on research in Physics Teaching. Among the most emphasized aspects in those reviews are: primary sources analysis and historical context regarding. We conclude that the detached aspects in the reviews are good criteria/parameters to be used to evaluate the production on HPS (paradidactic, scientific publishing, articles/essays) directed, mainly, to the University.  ; http://dx.doi.org/10.5007/2175-7941.2013v30n3p471O presente trabalho tem como objetivo investigar parâmetros para avaliar a produção literária em História e Filosofia da Ciência (HFC) voltada para o ensino e divulgação das ideias da Física, a partir dos aspectos positivos e negativos apontados por autores de resenhas de livros didáticos, paradidáticos, de divulgação científica e/ou de artigos/ensaios enfocando a HFC. Tais resenhas estão publicadas na literatura nacional de pesquisa em Ensino de Física. Dentre os pontos mais acentuados nas resenhas estão: análise de fontes primárias e consideração do contexto da época. Concluímos que os pontos destacados nas resenhas constituem bons critérios/parâmetros a serem utilizados para avaliar a produção em HFC (paradidáticos...