797 research outputs found
Heat Pumping in Nanomechanical Systems
No full textWe propose using a phonon pumping mechanism to transfer heat from a cold to a hot body using a propagating modulation of the medium connecting the two bodies. This phonon pump can cool nanomechanical systems without the need for active feedback. We compute the lowest temperature that this refrigerator can achieve.Fil: Chamon, Claudio. Boston University; Estados UnidosFil: Mucciolo, Eduardo R.. University Of Central Florida; Estados UnidosFil: Arrachea, Liliana del Carmen. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Capaz, Rodrigo B.. Universidade Federal do Rio de Janeiro; Brasi
Microscopic model of a phononic refrigerator
No full textWe analyze a simple microscopic model to pump heat from a cold to a hot reservoir in a nanomechanical system. The model consists of a one-dimensional chain of masses and springs coupled to a back gate through which a time-dependent perturbation is applied. The action of the gate creates a moving phononic barrier by locally pinning a mass. We solve the problem numerically using a nonequilibrium Green's function technique. For low driving frequencies and for sharp traveling barriers, we show that this microscopic model realizes a phonon refrigerator. © 2012 American Physical Society.Fil: Arrachea, Liliana del Carmen. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Mucciolo, Eduardo R.. University Of Central Florida; Estados UnidosFil: Chamon, Claudio. Boston University; Estados UnidosFil: Capaz, Rodrigo B.. Universidade Federal do Rio de Janeiro; Brasi
Straight to the bar: Molecular nanostructures, graphene, nanotubes. XXIst International Winterschool on Electronic Properties of Novel Materials (IWEPNM 2007), Kirchberg, Austria, 10–17 March 2007
No full textTight binding parametrization of few-layer black phosphorus from first-principles calculations
No full textReorganization Energy upon Controlled Intermolecular Charge‐Transfer Reactions in Monolithically Integrated Nanodevices
No full textIntermolecular electron-transfer reactions are key processes in physics, chemistry, and biology. The electron-transfer rates depend primarily on the system reorganization energy, that is, the energetic cost to rearrange each reactant and its surrounding environment when a charge is transferred. Despite the evident impact of electron-transfer reactions on charge-carrier hopping, well-controlled electronic transport measurements using monolithically integrated electrochemical devices have not successfully measured the reorganization energies to this date. Here, it is shown that self-rolling nanomembrane devices with strain-engineered mechanical properties, on-a-chip monolithic integration, and multi-environment operation features can overcome this challenge. The ongoing advances in nanomembrane-origami technology allow to manufacture the nCap, a nanocapacitor platform, to perform molecular-level charge transport characterization. Thereby, employing nCap, the copper-phthalocyanine (CuPc) reorganization energy is probed, ≈0.93 eV, from temperature-dependent measurements of CuPc nanometer-thick films. Supporting the experimental findings, density functional theory calculations provide the atomistic picture of the measured CuPc charge-transfer reaction. The experimental strategy demonstrated here is a consistent route towards determining the reorganization energy of a system formed by molecules monolithically integrated into electrochemical nanodevices
Multidialectal orthography and the writing of vowels in Mixe
No full textThis paper deals with the challenges of achieving a unified writing system for all Oaxaca Mixe languages, something that many community members deem necessary for defending the identity and culture of the Mixe people.
The Mixe orthography was created in the 80’s as the result of the collaboration between community members and linguists (cf. Valiñas, 1991). One explicit goal of that process was to create a single writing system for all the dialects. Nowadays, this system is a wide spread orthography as it is used almost officially in some communities, it appears in recent publications (Díaz, 2008; Zavala, 2013a, b; inter alia), and it is taught in some high schools and in two colleges throughout the Mixe territory. It is intended to be a deep orthography (Seifart, 2006; Katz & Frost, 1992; inter alia), with a high correspondence between phonemes and graphemes (Reyes, 2005). While it can be easily adapted to write the consonants for all dialects, it has several problems for writing vowels.
Due to the lack of phonological descriptions thirty years ago, the vowels systems of many Mixe languages were not taken into account. Furthermore, there was little understanding of the phonological processes that changed the vowel systems from six vowels in proto-Mixe (Wichmann, 1995) to a range of six to nine (or even ten) vowels in the present day Mixe languages (Author, forthcoming). Thus, it was difficult to realize that seemingly phonetically equivalent vowels are phonologically different across dialects and how differently sounding vowels are in fact phonologically equivalent between two given dialects. Thus, in many cases there is disagreement as to how some vowels should be represented. In addition, for some communities, using different conventions for writing vowels provides a distinctive identity (Suslak, 2003).
Based on a comparative study of the vowel system in twenty six Mixe dialects (Author, forthcoming), this paper shows how the problems for writing vowels could been solved once there was a better understanding of the phonological processes that changed the vowel systems in Mixe languages. However, this solution would involve a compromise between a deep and a shallow writing system. Finally, I will discuss how non-linguistic factors make very difficult to actually achieve the desire of having a unified orthography.
References
Author. Forthcoming. La evolución de los timbres vocálicos en lenguas mixes. Los efectos de la palatalización. México: Universidad Nacional Autónoma de México.
Díaz, J. G. 2008. Ii’pyxyukpët Ayuujk. México: CEA-UIIA
Katz, L. & R. Frost. 1992. The reading process is different for different orthograpies: The orthographic depth hypothesis. In Frost y Katz (eds.) Orthography, phonology, morphology, and meaning, pp. 67-84. Amsterdam: Elsevier.
Reyes, J. C. 2005. Aportes al proceso de enseñanza aprendizaje de la lectura y la escritura de la lengua ayuuk. Oaxaca, México: CEA-UIIA.
Seifart, F. 2006. Orthography development. In Gippert, Himmelmann & Mosel (eds.), Essentials of Language Documentation, pp. 275-299. Berlin: Walter de Gruyter.
Suslak, D. 2003. The story of ö: Orthography and cultural politics in the Mixe Highlands. Pragmatics 13 (4): 551-563.
Valiñas, L. 1991. Apuntes para una dialectología del mixe. Anales de Antroplogía 28: 437-456.
Wichmann, S. 1995. The relationship among the Mixe-Zoquean languages of Mexico. Salt Lake City: University of Utah Press.
Zavala, L. (comp.). 2013a. Nëwempët matya’aky. Aguilar (trad.). México: Ediciones del Hermitaño.
Zavala, L. (comp.). 2013b. Nëwempït matyä’äky. Comix (trad.). México: Ediciones del Hermitaño
Signatures of oxygen on Cu(3)Au(100): From isolated impurity to oxide regimes
No full textWe analyze the scanning tunneling microscopy (STM) signatures for the O/Cu(3)Au(100) surface from the low-coverage (isolated impurity) to high-coverage (oxide) regimes. First-principles calculations show that oxygen signatures switch from dark to bright spots as the oxygen coverage increases. This behavior is nicely traced back to a change in the oxygen orbital character of the Fermi-level electronic states. Our results allow for the chemical identification by STM of oxygen and copper atoms in the fully ordered O/Cu(3)Au(100)-c(2x2) surface.CNPq(FAPERJ) Fundacao de Amparo a Pesquisa do Estado do Rio de JaneiroFINE
Dynamic amplication in a periodic structure subject to a moving load passing a transition zone: Hyperloop case study
No full textHyperloop is an emerging high-speed transportation system in which air resistance is minimised by having the vehicle travel inside a de-pressurised tube supported by columns. This design leads to a strong periodic variation of the stiffness (among other parameters) experienced by the vehicle. Also, along its route, the Hyperloop will encounter so-called transition zones (e.g., junctions, bridges, etc.), where the properties (e.g., support stiffness) are different than for the rest of the structure. In railway engineering, increased degradation is seen in the vicinity of these transition zones, leading to increased frequency of maintenance. This work investigates response amplification mechanisms in a Hyperloop system that arise due to the combination of a transition zone and the structure having a periodic nature. The amplification mechanisms investigated here can help prevent degradation of the Hyperloop tube close to transition zones as well as fatigue and wear of the vehicle.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Dynamics of StructuresOffshore EngineeringEngineering Structure
Contribuições da Simulação Gerencial para o aprendizado de Ciências Contábeis
No full textTCC (graduação) - Universidade Federal de Santa Catarina, Centro Sócio Econômico, Curso de Ciências ContábeisA utilização da Simulação Gerencial no ensino é uma alternativa capaz de integrar teoria e prática. Neste sentido, avaliar contribuições promovidas pela aplicação deste método é relevante para seu planejamento, desenvolvimento e aplicação. Esta pesquisa procura identificar e mensurar as contribuições da utilização da Simulação Gerencial como método no processo de ensino-aprendizagem em Ciências Contábeis, na perspectiva dos acadêmicos. Para atingir este objetivo, utilizou-se o modelo proposto por Hense, Kriz e Wolfe (2009) que sugere uma avaliação holística da simulação. Como instrumento de coleta de dados, questionários com questões abertas e fechadas foram aplicados junto aos acadêmicos do curso de graduação em Ciências Contábeis da Universidade Federal de Santa Catarina. As respostas colhidas nos questionários foram analisadas de forma qualitativa e quantitativa. Destacam-se as contribuições observadas: a) a oportunidade de praticar habilidades gerenciais; b) a variação positiva para todos os itens pesquisados quanto ao nível de conhecimentos; c) o enriquecimento na interação entre colegas; d) o atendimento das expectativas frente ao método. Observa-se que a utilização da Simulação Gerencial estimula os participantes a exercitar habilidades necessárias ao seu desenvolvimento acadêmico e profissiona
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