Hydrodynamic correlation functions of a driven granular fluid in steady state

We study a homogeneously driven granular fluid of hard spheres at intermediate volume fractions and focus on time-delayed correlation functions in the stationary state. Inelastic collisions are modeled by incomplete normal restitution, allowing for efficient simulations with an event-driven algorithm. The incoherent scattering function Fincoh(q,t ) is seen to follow time-density superposition with a relaxation time that increases significantly as the volume fraction increases. The statistics of particle displacements is approximately Gaussian. For the coherent scattering function S(q,ω), we compare our results to the predictions of generalized fluctuating hydrodynamics, which takes into account that temperature fluctuations decay either diffusively or with a finite relaxation rate, depending on wave number and inelasticity. For sufficiently small wave number q we observe sound waves in the coherent scattering function S(q,ω) and the longitudinal current correlation function Cl(q,ω). We determine the speed of sound and the transport coefficients and compare them to the results of kinetic theory.

Development of a model-based transient calibration process for diesel engine electronic control module tables – Part 1: data requirements, processing, and analysis

This is the first part of a study investigating a model-based transient calibration process for diesel engines. The motivation is to populate hundreds of parameters (which can be calibrated) in a methodical and optimum manner by using model-based optimization in conjunction with the manual process so that, relative to the manual process used by itself, a significant improvement in transient emissions and fuel consumption and a sizable reduction in calibration time and test cell requirements is achieved. Empirical transient modelling and optimization has been addressed in the second part of this work, while the required data for model training and generalization are the focus of the current work. Transient and steady-state data from a turbocharged multicylinder diesel engine have been examined from a model training perspective. A single-cylinder engine with external air-handling has been used to expand the steady-state data to encompass transient parameter space. Based on comparative model performance and differences in the non-parametric space, primarily driven by a high engine difference between exhaust and intake manifold pressures (ΔP) during transients, it has been recommended that transient emission models should be trained with transient training data. It has been shown that electronic control module (ECM) estimates of transient charge flow and the exhaust gas recirculation (EGR) fraction cannot be accurate at the high engine ΔP frequently encountered during transient operation, and that such estimates do not account for cylinder-to-cylinder variation. The effects of high engine ΔP must therefore be incorporated empirically by using transient data generated from a spectrum of transient calibrations. Specific recommendations on how to choose such calibrations, how many data to acquire, and how to specify transient segments for data acquisition have been made. Methods to process transient data to account for transport delays and sensor lags have been developed. The processed data have then been visualized using statistical means to understand transient emission formation. Two modes of transient opacity formation have been observed and described. The first mode is driven by high engine ΔP and low fresh air flowrates, while the second mode is driven by high engine ΔP and high EGR flowrates. The EGR fraction is inaccurately estimated at both modes, while EGR distribution has been shown to be present but unaccounted for by the ECM. The two modes and associated phenomena are essential to understanding why transient emission models are calibration dependent and furthermore how to choose training data that will result in good model generalization.

Mass Transport Perspective on an Accelerated Exclusion Process: Analysis of Augmented Current and Unit-Velocity Phases

In an accelerated exclusion process (AEP), each particle can "hop" to its adjacent site if empty as well as "kick" the frontmost particle when joining a cluster of size ℓ⩽ℓ_{max}. With various choices of the interaction range, ℓ_{max}, we find that the steady state of AEP can be found in a homogeneous phase with augmented currents (AC) or a segregated phase with holes moving at unit velocity (UV). Here we present a detailed study on the emergence of the novel phases, from two perspectives: the AEP and a mass transport process (MTP). In the latter picture, the system in the UV phase is composed of a condensate in coexistence with a fluid, while the transition from AC to UV can be regarded as condensation. Using Monte Carlo simulations, exact results for special cases, and analytic methods in a mean field approach (within the MTP), we focus on steady state currents and cluster sizes. Excellent agreement between data and theory is found, providing an insightful picture for understanding this model system.

Testing the TICT State Hypothesis: an Investigation into the Solvatochromic Behavior of 2-Naphthalenylmethylene Malononitrile

Towards the goal of investigating the possible Twisted Intramolecular Charge Transfer (TICT) state mechanism of fluorescence emission, two aromatic dicyanovinyl compounds, 2-(naphthalene-2-ylmethylene) malononitrile (DCN) and a rigidified analogue, 3,4-dihydrophenanthren-1(2H)-ylidene)malononitrile (RDCN) were synthesized and their absorption and steady-state fluorescence emission spectra characterized. The spectral characterization was divided into two studies: first, DCN and RDCN were characterized in liquid solvents of increasing polarity; second, DCN and RDCN were characterized in viscous solvents and rigid glass media. The absorption spectra for both DCN and RDCN in all solvents demonstrated little to no solvatochromism. Emission results for DCN and RDCN in liquid solvents of increasing polarity showed DCN possessing strong solvatochromism while RDCN showed much less solvatochromism. Using the Lippert-Mataga equation, the difference between the ground and excited state dipole moment for DCN was estimated to be 8.4 + 0.4 Debye and between ~3.0 to 5.0 Debye for RDCN. Quantum yield measurements for DCN and RDCN in hexane, diethyl ether and acetonitrile were less than 0.01 and independent of polarity for both both solvents, with DCN generally possessing a quantum yield 3-4 times greater than RDCN. Experiments in glass media for DCN and RDCN showed a lessening of their solvatochromic character in both polar and non-polar glasses. These data provide strong evidence for a link between molecular flexibility and solvatochromism. However, while these data are consistent with a TICT state hypothesis for the emission mechanism, an alternative mechanism proposed by Maroncelli et al.10 involving rotation about the dicyanovinyl double bond in the excited state remains a possibility as well.