Molecular mechanics and molecular dynamics analysis of Drexler-Merkle gears and neon pump

Over the past two years at the Materials and Process Simulation Center, we have been developing simulation approaches for studying the molecular nanomachine designs pioneered by Drexler and Merkle. These nanomachine designs, such as planetary gears and neon pump, are described with atomistic details and involve up to 10 000 atoms. With the Dreiding and universal force fields, we have optimized the structures of the two planetary gear designs and the neon pump. At the Fourth Foresight conference, we reported rotational impulse dynamics studies of the first and second generation designs of planetary gears undergoing very high-frequency rotational motions. We will explore stability of these designs in the lower frequency regimes which require long time simulations. We will report the molecular mechanics and molecular dynamics simulations performed on these model systems. We explore the following modes in these studies: (1) impulse mode; (2) constant angular velocity - perpetual rotation; (3) constant torque - acceleration from rest

Nonadiabatic Study of Dynamic Electronic Effects during Brittle Fracture of Silicon

It has long been observed that brittle fracture of materials can lead to emission of high energy electrons and UV photons, but an atomistic description of the origin of such processes has lacked. We report here on simulations using a first-principles-based electron force field methodology with effective core potentials to describe the nonadiabatic quantum dynamics during brittle fracture in silicon crystal. Our simulations replicate the correct response of the crack tip velocity to the threshold critical energy release rate, a feat that is inaccessible to quantum mechanics methods or conventional force-field-based molecular dynamics. We also describe the crack induced voltages, current bursts, and charge carrier production observed experimentally during fracture but not previously captured in simulations. We find that strain-induced surface rearrangements and local heating cause ionization of electrons at the fracture surfaces

Effect of surface oxidation on the electronic transport properties of phosphorene gas sensors: a computational study

The potential for phosphorene-based devices has been compromised by the material's fast degradation under ambient conditions. Its tendency to fully oxidize under O₂-rich and humid environments, leads to the loss of its appealing semiconducting properties. However, partially-oxidized phosphorene (po-phosphorene), has been demonstrated to remain stable over significantly longer periods of time, thereby enabling its use in sensing applications. Here, we present a computational study of po-phosphorene-based gas sensors, using the Density-Functional-based Tight Binding (DFTB) method. We show that DFTB accurately predicts the bandgap for the pristine material and po-phosphorene, the electronic transport properties of po-phosphorene at different surface oxygen concentrations, and the appropriate trends in Density-of-States (DOS) contributions caused by adsorbed gas molecules, to demonstrate its potential application in the development of gas sensors. Results are compared against the more traditional and expensive Density Functional Theory (DFT) method using generalized gradient approximation (GGA) exchange–correlation functionals, which significantly underestimates the material's bandgap

El problema de los excluidos. las leyes contra la vagancia en colombia durante las décadas de 1820 a 1840

Este artículo investiga el fenómeno de la vagancia en Colombia durante las décadas de 1820 a 1840 a partir de un estudio de la legislación, en el cual se detallan los sujetos, las prácticas y las condenas. Dicho estudio se realiza en relación con el problema de la opinión pública y la construcción de una legitimidad política para la República. A través del análisis de la normatividad, los informes oficiales y la prensa, se rastrean las significaciones de la vagancia, las transformaciones y permanencias de las políticas contra esta y las discusiones dadas en relación con la pobreza y la exclusión. De esta manera, se busca dar cuenta de las consideraciones de esta en contraposición a las virtudes republicanas como un problema en que se articulan los campos de la moral, la economía y la política, y de cómo y por qué el vago se convirtió en sujeto de leyes y policía, quienes buscaron controlarlo y sujetarlo por medio de la instrucción, el trabajo y la colonización

El peligro de los otros: represión de esclavos en el suroccidente colombiano durante la primera mitad del siglo XIX

Durante la primera mitad del siglo XIX, la nueva república confirió algunos derechos a los esclavos, en un contexto de conflictos sociales entre esclavistas, esclavos y cimarrones. En este artículo explorao los conflictos políticos, militares y socioculturales entre las élites y los esclavos del suroccidente colombiano durante este periodo. Particularmente, analizo lamanera como los esclavos fueron considerados peligrosos por las élites con el propósito de justificar un aparataje de leyes e instituciones republicanas de control represivo, para preservar sus capitales y su poder. Esta investigación se basa en el análisis de archivos nacionales y regionales, de prensa, comunicados y documentación oficial, casos criminales, leyes, cartas, escritos y memorias.In the early to mid-19th century, the new Colombian republic granted some rights to slaves, during a period rent by social conflict among slave-owners, slaves, and maroons. Based on the analysis of national and regional archives, press archives, official communiqués and documents, criminal cases, laws, letters, texts, and memoirs, this article, examines the political,military, and sociocultural confrontations between elites and slaves in southwestern Colombia during that period. The analysis focuses particularly on how the elites labelled the slaves as dangerous in order to justify a repressive legal and institutional control designed to preserve their capital and power.Durante a primeira metade do século xix, a nova república conferiu alguns direitos aos escravos, num contexto de conflitos sociais entre escravistas, escravos e escravos fugidos. Neste artigo, exploro os conflitos políticos, militares esocioculturais entre as elites e os escravos do sudoeste colombiano durante esse período. Particularmente, analiso a maneira como os escravos foram considerados perigosos pelas elites com o propósito de justificar um conjunto de leis e instituições republicanas de controle repressor, para preservar seus capitais e seu poder. Esta pesquisa baseia-se naanálise de arquivos nacionais e regionais, de imprensa, comunicados e documentação oficial, casos criminais, leis, cartas, escritos e memórias

Control social en Colombia 1820-1850: vagos, prostitutas y esclavos

La presente investigación reconstruye y analiza el problema del control social hacia los pobres en Colombia entre 1820 y 1850, y tiene como eje central el problema de la vagancia y su articulación a los problemas de la mendicidad, la prostitución y la esclavitud. A partir del análisis de las constituciones, la normatividad, los juicios criminales, y fuentes secundarias referente a la pobreza y el problema de lo social, intentaré aproximarme a las estrategias de intervención, la policía, los sujetos señalados como vagos, las prostitutas y los esclavos, y sus juicios criminales y las sentencias que sufrieron, situándolos en la historia y los conflictos económicos, políticos y culturales de su tiempo. Este proyecto se inscribe en la historia socio-cultural y específicamente en el programa de historia de la protección social.Abstract. This research analyses the problem of social control towards poor people in Colombia between the years 1820 and 1850, its main concern is vagrancy and its articulation to the problems of mendicity, prostitution and slavery. From the analysis of the constitutions, normativeness, criminal judgements, and secondary sources referring to poverty and the problem of the social, I will attempt to approach the ways of social intervention the police, the people label as vagrants, prostitutes and slaves, and the condemnation they went through being placed in history and the economic, political and cultural conflicts of their time. This Project can be classed in Sociocultural History, specifically in the program of the history of social protection.Maestrí

Diseño de vestuario femenino inspirado en una cultura, donde el elemento que prime sea la seducción

Este proyecto busca explorar elementos de la seducción tanto actuales como pasados, que aplicados al vestuario, le faciliten a la mujer que lo lleva puesto, relacionarse con personas del otro género en entornos sociales. La seducción es un tema que esta biológicamente implícito en los seres humano, ya que facilita el acercamiento de las personas, y esto a su vez, aumenta las posibilidades de supervivencia de la especie. La seducción es un intercambio de signos, tanto verbales como no verbales que se da entre una pareja. La autoestima y la confianza juegan un papel importante en este tema, permitiéndole a la mujer mostrarse tal cual es. El Vestuario es una extensión del lenguaje corporal, lo cual lo hace un campo de acción valido para explorar en pro de facilitar esta interacción. La cultura Minoica fue una cultura que se dio a orillas del mar Egeo, en esta cultura se puede apreciar como el tema del vestuario, de la sensualidad y del cuerpo, es un tema importante tanto en el pasado como en la actualidad, es por esto que este proyecto busca extraer elementos de ella, para traerlos a la actualidad con este mismo propósito.Diseñador (a) IndustrialPregrad

General Multiobjective Force Field Optimization Framework, with Application to Reactive Force Fields for Silicon Carbide

First-principles-based force fields prepared from large quantum mechanical data sets are now the norm in predictive molecular dynamics simulations for complex chemical processes, as opposed to force fields fitted solely from phenomenological data. In principle, the former allow improved accuracy and transferability over a wider range of molecular compositions, interactions, and environmental conditions unexplored by experiments. That is, assuming they have been optimally prepared from a diverse training set. The trade-off has been force field engines that are functionally complex, with a large number of nonbonded and bonded analytical forms that give rise to rather large parameter search spaces. To address this problem, we have developed GARFfield (genetic algorithm-based reactive force field optimizer method), a hybrid multiobjective Pareto-optimal parameter development scheme based on genetic algorithms, hill-climbing routines and conjugate-gradient minimization. To demonstrate the capabilities of GARFfield we use it to develop two very different force fields: (1) the ReaxFF reactive force field for modeling the adiabatic reactive dynamics of silicon carbide growth from an methyltrichlorosilane precursor and (2) the SiC electron force field with effective core pseudopotentials for modeling nonadiabatic dynamic phenomena with highly excited electronic states. The flexible and open architecture of GARFfield enables efficient and fast parallel optimization of parameters from quantum mechanical data sets for demanding applications like ReaxFF, electronic fast forward (or electron force field), and others including atomistic reactive charge-optimized many-body interatomic potentials, Morse, and coarse-grain force fields