1,251 research outputs found

    Tuning the conductance of a molecular switch

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    The ability to control the conductance of single molecules will have a major impact in nanoscale electronics. Azobenzene, a molecule that changes conformation as a result of a trans/cis transition when exposed to radiation, could form the basis of a light-driven molecular switch. It is therefore crucial to clarify the electrical transport characteristics of this molecule. Here, we investigate theoretically charge transport in a system in which a single azobenzene molecule is attached to two carbon nanotubes. In clear contrast to gold electrodes, the nanotubes can act as true nanoscale electrodes and we show that the low-energy conduction properties of the junction may be dramatically modified by changing the topology of the contacts between the nanotubes and the molecules, and/or the chirality of the nanotubes (that is, zigzag or armchair). We propose experiments to demonstrate controlled electrical switching with nanotube electrodes

    Spin transport in helical biological systems

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    Motivated by the recent experimental demonstration of spin selective effects in monolayers of double-stranded DNA oligomers, our work presents a minimal model to describe electron transmission through helical fields. Our model highlight that the lack of inversion symmetry due to the chirality of the potential is a key factor which will lead to a high spin-polarization (SP). We also study the stability of the SP against fluctuations of the electronic structure induced by static disorder affecting the on-site energies. In the energy regions where the spin- filtering occurs, our results remain stable against moderate disorders although the SP is slightly reduced

    Urban Cargo Transport UAV Final Design Review

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    Delivery of goods to homes and offices over the last decades has seen a significant increase as more people and businesses need or want items sent directly to them. With the increase in demand, technology has also experienced a rapid growth, specifically in the field of unmanned aerial vehicles (UAVs). Many major companies are currently researching UAVs as the future of their delivery operations. With this ever-growing demand, NASA has issued a design competition of a UAV developed for urban deliveries. This unmanned aircraft system (UAS) would need to be able to deliver small packages, in a timely manner, within the city they operate. They must be able to drop off two lightweight packages to destinations without human intervention. They must be safe for the citizens of the cities they operate in and output low levels of sound as to not add to the noise pollution (4.4 Design Requirements and Specifications:). Various areas of development needed to be considered and analyzed. The UAV body has fixed wings with a boom-tail design and a multi-rotor configuration for the motors (Figure 7). The body of the aircraft underwent analysis in SolidWorks to gather data of its aerodynamics (5.3 Computational Fluid Simulation). With this analysis, the MH-83-iL airfoil was chose to best suit the needs of this craft (3.2.1 Main Airfoil). Through wing loading analysis, NRT’s UAV would be able to fly at cruising speed of 27 knots and have a 0.08 thrust. Other aspects to consider included control systems, budgetary analysis, and government regulations. Controls systems provide data and insurance for collision avoidance, altitude readings, thermal sensors, and GPS guidance. These systems as well as a safety parachute allow for maximum performance and precaution to help integrate it into urban life. The cost of the aircraft (4.7 Budget) comes out to roughly $1700 given our required body, systems, and propulsion systems. Lastly, government regulations with the Federal Aviation Administration (FAA) provide guidelines for registering and flying UAVs in urban environments. Working closely with the FAA would be required to ensure all federal laws are abided by. The development of and advancement of the urban air mobility (UAM) can provide a more efficient and cost-effective means of delivering packages for companies throughout the nation. This can be achieved with computational and budgetary analysis that best optimize UAV, along with proper safety and government regulations, for company use

    Literatura e arte contemporânea

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    O artigo explora as relações entre a literatura e as práticas da arte contemporânea focando em autores como Enrique Vila-Matas, César Aira, Mario Bellatin e Kennet Goldsmith. Técnicas de montagem, apropriação, transcrição, performance aparecem como chaves para compreender os caminhos seguidos por alguns autores contemporâneos que sentem de novo um certo impasse na escrita literária

    Perfil emprendedor de un grupo de alumnos del último año de una especialidad de negocios y otra de ingeniería de la Pontificia Universidad Católica del Perú en el año 2017

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    El presente estudio plantea la necesidad de conocer cuál es el perfil emprendedor de un grupo de alumnos de una especialidad de negocios y una de ingeniería, determinando qué factores son importantes para constituir un perfil emprendedor y tomando como base un cuestionario validado; además de una serie de entrevistas a los alumnos para profundizar en ciertos factores evaluados en el cuestionario. La aproximación de la investigación se realiza mediante el estudio de caso de dos grupos de alumnos pertenecientes a una especialidad de negocios y otra de ingeniería de la Pontificia Universidad Católica del Perú. En consecuencia, la presente investigación describe la situación actual de los dos grupos de alumnos, su predisposición al emprendimiento en base a los factores mostrados, todo ello enmarcado en un modelo teórico. Como resultado de este estudio, se elabora un perfil emprendedor de los grupos de alumnos. Este sintetiza los hallazgos de la investigación, y facilita la descripción de las características más adecuadas para impulsar el perfil emprendedor de los alumnos. Finalmente, como resultado de la descripción del cuestionario y análisis de las entrevistas se presentan conclusiones y recomendaciones relativas a mejoras en el desarrollo del perfil emprendedor de los alumnos.Tesi

    Computational Design of Nanomaterials

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    The development of materials with tailored functionalities and with continuously shrinking linear dimensions towards (and below) the nanoscale is not only going to revolutionize state of the art fabrication technologies, but also the computational methodologies used to model the materials properties. Specifically, atomistic methodologies are becoming increasingly relevant in the field of materials science as a fundamental tool in gaining understanding on as well as for pre-designing (in silico material design) the behavior of nanoscale materials in response to external stimuli. The major long-term goal of atomistic modelling is to obtain structure-function relationships at the nanoscale, i.e. to correlate a definite response of a given physical system with its specific atomic conformation and ultimately, with its chemical composition and electronic structure. This has clearly its pendant in the development of bottom-up fabrication technologies, which also require a detailed control and fine tuning of physical and chemical properties at sub-nanometer and nanometer length scales. The current work provides an overview of different applications of atomistic approaches to the study of nanoscale materials. We illustrate how the use of first-principle based electronic structure methodologies, quantum mechanical based molecular dynamics, and appropriate methods to model the electrical and thermal response of nanoscale materials, provides a solid starting point to shed light on the way such systems can be manipulated to control their electrical, mechanical, or thermal behavior. Thus, some typical topics addressed here include the interplay between mechanical and electronic degrees of freedom in carbon based nanoscale materials with potential relevance for designing nanoscale switches, thermoelectric properties at the single-molecule level and their control via specific chemical functionalization, and electrical and spin-dependent properties in biomaterials. We will further show how phenomenological models can be efficiently applied to get a first insight in the behavior of complex nanoscale systems, for which first principle electronic structure calculations become computationally expensive. This will become especially clear in the case of biomolecular systems and organic semiconductors
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