Relation between boundary slip mechanisms and water-like fluid behavior

The slip of a fluid layer in contact with a solid confining surface is investigated for different temperatures and densities using molecular dynamic simulations. We show that for an anomalous water-like fluid the slip goes as follows: for low levels of shear, the defect slip appears and is related with the particle exchange between the fluid layers; at high levels of shear, the global slip occurs and is related to the homogeneous distribution of the fluid in the confining surfaces. The oscillations in the transition velocity from the defect to the global slip is shown to be associated with changes in the layering distribution in the anomalous fluid.Comment: 20 pages, 12 figures, accepted by Physical Review E in 27 february 201

Multiple liquid-liquid critical points and anomalies in core-softened potentials

The relation between liquid-liquid phase transitions and waterlike density anomalies in core-softened potentials of fluids was investigated in an exactly solvable one dimensional lattice model and a in a three dimensional fluid with fermi-like potential, the latter by molecular dynamics. Both systems were shown to present three liquid phases, two liquid-liquid phase transitions closely connected to two distinct regions of anomalous density increase. We propose that an oscillatory behavior observed on the thermal expansion coefficient as a function of pressure can be used as a signature of the connection between liquid-liquid phase and density

Entropy, diffusivity and the energy landscape of a water-like fluid

Molecular dynamics simulations and instantaneous normal mode (INM) analysis of a fluid with core-softened pair interactions and water-like liquid-state anomalies are performed to obtain an understanding of the relationship between thermodynamics, transport properties and the poten- tial energy landscape. Rosenfeld-scaling of diffusivities with the thermodynamic excess and pair correlation entropy is demonstrated for this model. The INM spectra are shown to carry infor- mation about the dynamical consequences of the interplay between length scales characteristic of anomalous fluids, such as bimodality of the real and imaginary branches of the frequency distribu- tion. The INM spectral information is used to partition the liquid entropy into two contributions associated with the real and imaginary frequency modes; only the entropy contribution from the imaginary branch captures the non-monotonic behaviour of the excess entropy and diffusivity in the anomalous regime of the fluid

Core-softened fluids, water-like anomalies, and the liquid-liquid critical points

Molecular dynamics simulations are used to examine the relationship between water-like anomalies and the liquid-liquid critical point in a family of model fluids with multi-Gaussian, core-softened pair interactions. The core-softened pair interactions have two length scales, such that the longer length scale associated with a shallow, attractive well is kept constant while the shorter length scale associated with the repulsive shoulder is varied from an inflection point to a minimum of progressively increasing depth. The maximum depth of the shoulder well is chosen so that the resulting potential reproduces the oxygen-oxygen radial distribution function of the ST4 model of water. As the shoulder well depth increases, the pressure required to form the high density liquid decreases and the temperature up to which the high-density liquid is stable increases, resulting in the shift of the liquid-liquid critical point to much lower pressures and higher temperatures. To understand the entropic effects associated with the changes in the interaction potential, the pair correlation entropy is computed to show that the excess entropy anomaly diminishes when the shoulder well depth increases. Excess entropy scaling of diffusivity in this class of fluids is demonstrated, showing that decreasing strength of the excess entropy anomaly with increasing shoulder depth results in the progressive loss of water-like thermodynamic, structural and transport anomalies. Instantaneous normal mode analysis was used to index the overall curvature distribution of the fluid and the fraction of imaginary frequency modes was shown to correlate well with the anomalous behavior of the diffusivity and the pair correlation entropy. The results suggest in the case of core-softened potentials, in addition to the presence of two length scales, energetic, and entropic effects associated with local minima and curvatures of the pair interaction play an important role in determining the presence of water-like anomalies and the liquid-liquid phase transition

Water diffusion in carbon nanotubes : Interplay between confinement, surface deformation, and temperature

In this article, we investigate, through molecular dynamics simulations, the diffusion behavior of the TIP4P/2005 water confined in pristine and deformed carbon nanotubes (armchair and zigzag). To analyze different diffusive mechanisms, the water temperature was varied as 210 ≤ T ≤ 380 K. The results of our simulations reveal that water presents a non-Arrhenius to Arrhenius diffusion crossover. The confinement shifts the diffusion transition to higher temperatures when compared with the bulk system. In addition, for narrower nanotubes, water diffuses in a single line, which leads to its mobility independent of the activation energy

Water diffusion in rough carbon nanotubes

We use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes with different degrees of deformation at 300 K. We found that the number of hydrogen bonds that water forms depends on nanotube topology, leading to enhancement or suppression of water diffusion. The simulation results reveal that more realistic nanotubes should be considered to understand the confined water diffusion behavior, at least for the narrowest nanotubes, when the interaction between water molecules and carbon atoms is relevant

Implementación de control interno en el proceso de producción de hilado en la empresa El Telar S.A. en el periodo 2015

La presente tesina tiene como objetivo, determinar implicancias positivas del control interno en el proceso productivo de hilado en la empresa El Telar S.A., la eficacia y eficiencia en las operaciones, reduciendo riesgos en la generación de información veraz y oportuna. En la metodología, se aplicó el diseño no experimental, transeccional – descriptivo, el método empleado es el inductivo y de análisis. El tipo de investigación utilizado es el de campo. El método de observación fue cuantitativo, y el instrumento aplicado fue el cuestionario. Se emplearon técnicas para la recopilación de información, como por ejemplo la encuesta y el flujograma, los cuales se llevaron a cabo mediante visitas al área de producción, indagando y observando los sub procesos de hilado, con la finalidad de identificar cuáles eran las falencias en esta área. Se hizo un cuestionario para el personal, del cual un aproximado del 65% responde de manera incorrecta, denotando así que no se ha estado aplicando de forma correcta el control interno en los 12 sub-procesos de hilado; lo cual genera que no se logre alcanzar los objetivos trazados. De esta manera, se analizó la situación actual en el área de producción en la empresa El Telar S.A., observando los procesos existentes, identificando riesgos e implementando controles que mejoren el control interno ya existente. Existe un riesgo residual, el cual se mantiene en el proceso productivo, sin embargo, gracias al monitoreo de cada control analizado y propuesto se puede mantener una adecuada gestión.Trabajo de suficiencia profesionalCampus Lima Centr

Nanoscale sliding friction versus commensuration ratio : molecular dynamics simulations

The pioneer work of Krim and Widom [Phys. Rev. B 38, 12184 (1988)] unveiled the origin of the viscous nature of friction at the atomic scale. This generated extensive experimental and theoretical activity. However, fundamental questions remain open like the relation between sliding friction and the topology of the substrate, as well as the dependence on the temperature of the contact surface. Here we present results, obtained using molecular dynamics, for the phononic friction coefficient (nph) for a one-dimensional model of an adsorbatesubstrate interface. Different commensuration relations between adsorbate and substrate are investigated as well as the temperature dependence of nph. In all the cases we studied nph depends quadratically on the substrate corrugation amplitude, but is a nontrivial function of the commensuration ratio between substrate and adsorbate. The most striking result is a deep and wide region of small values of nph for substrate-adsorbate commensuration ratios between ≈0.65 and 0.9. Our results shed some light on contradictory results for the relative size of phononic and electronic friction found in the literature

Nanoscale sliding friction versus commensuration ratio : molecular dynamics simulations

The pioneer work of Krim and Widom [Phys. Rev. B 38, 12184 (1988)] unveiled the origin of the viscous nature of friction at the atomic scale. This generated extensive experimental and theoretical activity. However, fundamental questions remain open like the relation between sliding friction and the topology of the substrate, as well as the dependence on the temperature of the contact surface. Here we present results, obtained using molecular dynamics, for the phononic friction coefficient (nph) for a one-dimensional model of an adsorbatesubstrate interface. Different commensuration relations between adsorbate and substrate are investigated as well as the temperature dependence of nph. In all the cases we studied nph depends quadratically on the substrate corrugation amplitude, but is a nontrivial function of the commensuration ratio between substrate and adsorbate. The most striking result is a deep and wide region of small values of nph for substrate-adsorbate commensuration ratios between ≈0.65 and 0.9. Our results shed some light on contradictory results for the relative size of phononic and electronic friction found in the literature