First-passage time theory of activated rate chemical processes in electronic molecular junctions

Confined nanoscale spaces, electric fields and tunneling currents make the molecular electronic junction an experimental device for the discovery of new, out-of-equilibrium chemical reactions. Reaction-rate theory for current-activated chemical reactions is developed by combining a Keldysh nonequilibrium Green's functions treatment of electrons, Fokker-Planck description of the reaction coordinate, and Kramers' first-passage time calculations. The NEGF provide an adiabatic potential as well as a diffusion coefficient and temperature with local dependence on the reaction coordinate. Van Kampen's Fokker-Planck equation, which describes a Brownian particle moving in an external potential in an inhomogeneous medium with a position-dependent friction and diffusion coefficient, is used to obtain an analytic expression for the first-passage time. The theory is applied to several transport scenarios: a molecular junction with a single, reaction coordinate dependent molecular orbital, and a model diatomic molecular junction. We demonstrate the natural emergence of Landauer's blowtorch effect as a result of the interplay between the configuration dependent viscosity and diffusion coefficients. The resultant localized heating in conjunction with the bond-deformation due to current-induced forces are shown to be the determining factors when considering chemical reaction rates; each of which result from highly tunable parameters within the system

Emergence of negative viscosities and colored noise under current-driven Ehrenfest molecular dynamics

Molecules in molecular junctions are subject to current-induced forces that can break chemical bonds, induce reactions, destabilize molecular geometry, and halt the operation of the junction. Theories behind current-driven molecular dynamics simulations rely on a perturbative time-scale separation within the system with subsequent use of nonequilibrium Green's functions (NEGF) to compute conservative, non-conservative, and stochastic forces exerted by electrons on nuclear degrees of freedom. We analyze the effectiveness of this approximation, paying particular attention to the phenomenon of negative viscosities. The perturbative approximation is directly compared to the nonequilibrium Ehrenfest approach. We introduce a novel time-stepping approach to calculate the forces present in the Ehrenfest method via exact integration of the equations of motion for the nonequilibrium Green's functions, which does not necessitate a time-scale separation within the system and provides an exact description for the corresponding classical dynamics. We observe that negative viscosities are not artifacts of a perturbative treatment but also emerge in Ehrenfest dynamics. However, the effects of negative viscosity have the possibility of being overwhelmed by the predominantly positive dissipation due to the higher-order forces unaccounted for by the perturbative approach. Additionally, we assess the validity of the white-noise approximation for the stochastic forces, finding that it is justifiable in the presence of a clear time-scale separation and is more applicable when the current-carrying molecular orbital is moved outside of the voltage window. Finally, we demonstrate the method for molecular junction models consisting of one and two classical degrees of freedom

Predicting turning points

This paper presents a new method for predicting turning points. The paper formally defines a turning point; develops a probit model for estimating the probability of a turning point; and then examines both the in-sample and out-of-sample forecasting performance of the model. The model performs better than some other methods for predicting turning points.Econometric models

Testing the chilling- before drought-tolerance hypothesis in Pooideae grasses

publishedVersio

Jumping-Droplet Electrostatic Energy Harvesting

Micro- and nanoscale wetting phenomena has been an active area of research due to its potential for improving engineered system performance involving phase change. With the recent advancements in micro/nanofabrication techniques, structured surfaces can now be designed to allow condensing coalesced droplets to spontaneously jump off the surface due to the conversion of excess surface energy into kinetic energy. In addition to being removed at micrometric length scales (~10 μm), jumping water droplets also attain a positive electrostatic charge (~10-100 fC) from the hydrophobic coating/condensate interaction. In this work, we take advantage of this droplet charging to demonstrate jumping-droplet electrostatic energy harvesting. The charged droplets jump between superhydrophobic copper oxide and hydrophilic copper surfaces to create an electrostatic potential and generate power during formation of atmospheric dew. We demonstrated power densities of ~15 pW/cm[superscript 2], which, in the near term, can be improved to ~1 μW/cm[superscript 2]. This work demonstrates a surface engineered platform that promises to be low cost and scalable for atmospheric energy harvesting and electric power generation.United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-FG02-09ER46577)United States. Office of Naval ResearchNational Science Foundation (U.S.). Graduate Research Fellowship Program (Grant 1122374

University Band Symphonic Band

Braden Auditorium Wednesday Evening November 16, 1994 8:00p.m

Ambient-mediated wetting on smooth surfaces

A consensus was built in the first half of the 20th century, which was further debated more than 3 decades ago, that the wettability and condensation mechanisms on smooth solid surfaces are modified by the adsorption of organic contaminants present in the environment. Recently, disagreement has formed about this topic once again, as many researchers have overlooked contamination due to its difficulty to eliminate. For example, the intrinsic wettability of rare earth oxides has been reported to be hydrophobic and non-wetting to water. These materials were subsequently shown to display dropwise condensation with steam. Nonetheless, follow on research demonstrated that the intrinsic wettability of rare earth oxides is hydrophilic and wetting to water, and that a transition to hydrophobicity occurs in a matter of hours-to-days as a consequence of the adsorption of volatile organic compounds from the ambient environment. The adsorption mechanisms, kinetics, and selectivity of these volatile organic compounds are empirically known to be functions of the substrate material and structure. However, these mechanisms, which govern the surface wettability, remain poorly understood. In this contribution, we introduce current research demonstrating the different intrinsic wettability of metals, rare earth oxides, and other smooth materials, showing that they are intrinsically hydrophilic. Then we provide details on research focusing on the wetting to non-wetting transition to hydrophobicity due to adsorption of volatile organic compounds. A state-of-the-art figure of merit mapping the wettability of different smooth solid surfaces to ambient exposure and surface carbon content is developed. In addition, we analyse recent works that address the wetting transitions so to shed light on how such processes affect droplet pinning and lateral adhesion. We then conclude with objective perspectives about research on wetting to non-wetting transitions on smooth solid surfaces in an attempt to raise awareness regarding surface contamination within the engineering, interfacial science, and physical chemistry domains

Responses of a wetland ecosystem to the controlled introduction of invasive fish

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136368/1/fwb12900_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136368/2/fwb12900.pd

Multisensory processing and proprioceptive plasticity during resizing illusions

Bodily resizing illusions typically use visual and/or tactile inputs to produce a vivid experience of one’s body changing size. Naturalistic auditory input (an input that reflects the natural sounds of a stimulus) has been used to increase illusory experience during the rubber hand illusion, whilst non-naturalistic auditory input can influence estimations of finger length. We aimed to use a non-naturalistic auditory input during a hand-based resizing illusion using augmented reality, to assess whether the addition of an auditory input would increase both subjective illusion strength and measures of performance-based tasks. Forty-four participants completed the following three conditions: no finger stretching, finger stretching without tactile feedback and finger stretching with tactile feedback. Half of the participants had an auditory input throughout all the conditions, whilst the other half did not. After each condition, the participants were given one of the following three performance tasks: stimulated (right) hand dot touch task, non-stimulated (left) hand dot touch task, and a ruler judgement task. Dot tasks involved participants reaching for the location of a virtual dot, whereas the ruler task concerned estimates of the participant’s own finger on a ruler whilst the hand was hidden from view. After all trials, the participants completed a questionnaire capturing subjective illusion strength. The addition of auditory input increased subjective illusion strength for manipulations without tactile feedback but not those with tactile feedback. No facilitatory effects of audio were found for any performance task. We conclude that adding auditory input to illusory finger stretching increased subjective illusory experience in the absence of tactile feedback but did not affect performance-based measures