Strategy for reducing molecular ensemble size for efficient rheological modeling of commercial polymers

2021 ◽  
Vol 65 (1) ◽  
pp. 43-57
Author(s):  
Yanan Gong ◽  
Valeriy Ginzburg ◽  
Sylvie Vervoort ◽  
Jaap Den Doelder ◽  
Ronald G. Larson
Keyword(s):  
Ensemble Size ◽  
Rheological Modeling ◽  
Commercial Polymers ◽  
Molecular Ensemble

scholarly journals Multiphoton Excitation of Organic Molecules in a Cavity – Superradiance as a Measure of Coherence

2020 ◽  
Author(s):  
Inga Ulusoy ◽  
Johana A. Gomez ◽  
Oriol Vendrell
Keyword(s):  
Organic Molecules ◽  
Broad Band ◽  
Decay Process ◽  
Ensemble Size ◽  
Radiation Mode ◽  
Collective Response ◽  
Long Time ◽  
Pulse Characteristics ◽  
Collective Emission ◽  
Molecular Ensemble

<div>Coherent excitation of a molecular ensemble coupled to a common radiation mode can lead to the collective emission of radiation known as superradiance. This collective emission only occurs if there is an entanglement between the molecules in their ground and excited state and can therefore serve as a macroscopic measure of coherence in the ensemble. Reported here are wave packet propagations for various pyrazine models of increasing complexity and molecular ensembles thereof. We show that ensemble coherence upon photoexcitation can prevail up to relatively long time scales, although the effect can diminish quickly with increasing ensemble size. Coherence can also build up over time and even reemerge after the molecules have passed through a conical intersection. The effect of the pump-pulse characteristics on the collective response of the molecular ensemble is also studied. A broad-band pulse imprints a large amount of initial coherence to the system, as compared to a longer pulse with a smaller spread in the frequency domain. However, the differential effects arising from a different pulse duration and coherent bandwidth become less prominent if the emission of light from the ensemble takes place after a non-adiabatic decay process.</div>

scholarly journals Multiphoton Excitation of Organic Molecules in a Cavity – Superradiance as a Measure of Coherence

2020 ◽  
Author(s):  
Inga Ulusoy ◽  
Johana A. Gomez ◽  
Oriol Vendrell
Keyword(s):  
Organic Molecules ◽  
Broad Band ◽  
Decay Process ◽  
Ensemble Size ◽  
Radiation Mode ◽  
Collective Response ◽  
Long Time ◽  
Pulse Characteristics ◽  
Collective Emission ◽  
Molecular Ensemble

<div>Coherent excitation of a molecular ensemble coupled to a common radiation mode can lead to the collective emission of radiation known as superradiance. This collective emission only occurs if there is an entanglement between the molecules in their ground and excited state and can therefore serve as a macroscopic measure of coherence in the ensemble. Reported here are wave packet propagations for various pyrazine models of increasing complexity and molecular ensembles thereof. We show that ensemble coherence upon photoexcitation can prevail up to relatively long time scales, although the effect can diminish quickly with increasing ensemble size. Coherence can also build up over time and even reemerge after the molecules have passed through a conical intersection. The effect of the pump-pulse characteristics on the collective response of the molecular ensemble is also studied. A broad-band pulse imprints a large amount of initial coherence to the system, as compared to a longer pulse with a smaller spread in the frequency domain. However, the differential effects arising from a different pulse duration and coherent bandwidth become less prominent if the emission of light from the ensemble takes place after a non-adiabatic decay process.</div>

scholarly journals Parameters Estimation and Prediction of Water Movement and Solute Transport in Layered, Variably Saturated Soils Using the Ensemble Kalman Filter

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1520
Author(s):  
Zheng Jiang ◽  
Quanzhong Huang ◽  
Gendong Li ◽  
Guangyong Li
Keyword(s):  
Kalman Filter ◽  
Solute Transport ◽  
Ensemble Kalman Filter ◽  
Water Movement ◽  
Parameters Estimation ◽  
Saturated Soils ◽  
Hydrological Models ◽  
State Variables ◽  
Ensemble Size ◽  
Highly Nonlinear

The parameters of water movement and solute transport models are essential for the accurate simulation of soil moisture and salinity, particularly for layered soils in field conditions. Parameter estimation can be achieved using the inverse modeling method. However, this type of method cannot fully consider the uncertainties of measurements, boundary conditions, and parameters, resulting in inaccurate estimations of parameters and predictions of state variables. The ensemble Kalman filter (EnKF) is well-suited to data assimilation and parameter prediction in Situations with large numbers of variables and uncertainties. Thus, in this study, the EnKF was used to estimate the parameters of water movement and solute transport in layered, variably saturated soils. Our results indicate that when used in conjunction with the HYDRUS-1D software (University of California Riverside, California, CA, USA) the EnKF effectively estimates parameters and predicts state variables for layered, variably saturated soils. The assimilation of factors such as the initial perturbation and ensemble size significantly affected in the simulated results. A proposed ensemble size range of 50–100 was used when applying the EnKF to the highly nonlinear hydrological models of the present study. Although the simulation results for moisture did not exhibit substantial improvement with the assimilation, the simulation of the salinity was significantly improved through the assimilation of the salinity and relative solutetransport parameters. Reducing the uncertainties in measured data can improve the goodness-of-fit in the application of the EnKF method. Sparse field condition observation data also benefited from the accurate measurement of state variables in the case of EnKF assimilation. However, the application of the EnKF algorithm for layered, variably saturated soils with hydrological models requires further study, because it is a challenging and highly nonlinear problem.

Role of the Interphase in the Interfacial Flow Stability in Coextrusion of Compatible Multilayered Polymers

2013 ◽  
Vol 554-557 ◽  
pp. 1738-1750 ◽  
Author(s):  
Hua Gui Zhang ◽  
Khalid Lamnawar ◽  
Abderrahim Maazouz
Keyword(s):  
Shear Stress ◽  
Viscosity Ratio ◽  
Flow Instability ◽  
Interfacial Shear Stress ◽  
Flow Stability ◽  
Interfacial Shear ◽  
Interfacial Instability ◽  
Interfacial Flow ◽  
Rheological Modeling

This work aims to highlight the importance of interphase triggered from interdiffusion at neighboring layers on controlling the interfacial flow instability of multilayer coextrusion based on a compatible bilayer system consist of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) melt streams. A fundamental rheological measurement on the bilayer structures provides a good strategy to probe the mutual diffusion process occurred at neighboring layers and to quantify the rheology and thickness of the interphase generated thereof. By implementing steady shear measurements on the multilayer’s, subtle interfacial slippage can be observed at a condition of short welding time and rather high shear rate due to the disentanglement of chains at the interphase. Pre-shear at an early stage on the multilayer was found to greatly promote the homogenizing process by inducing branched structures and hence increasing interfacial area. In coextrusion, some key classical decisive parameters concerning the interfacial instability phenomena such as viscosity ratio, thickness ratio and elasticity ratio, etc. were highlighted. These key factors that are significant in controlling the interfacial stability of coextrusion in an incompatible system seem not that important in a compatible system. In comparison to the severe flow instability observed in the coextrusion of PMMA/PE incompatible bilayer, the coextrusion of PMMA/PVDF compatible bilayer appears to be smooth without apparent interfacial flow instability due to the presence of the interphase. Interdiffusion can reduce (even eliminate) the interfacial flow instability of coextrusion despite of the very high viscosity ratio of PVDF versus PMMA at low temperatures. Indeed, in the coextrusion process, on one hand, the interdiffusion should be studied by taking into account of the effect of polymer chain orientation which was demonstrated to decelerate the diffusion coefficient. On the other hand, the interfacial shear stress was able to promote mixing and homogenizing process at the interface, which favours the development of the interphase and guarantees the stable interfacial flow. The degree of the interphase is related to a lot of parameters like contact time, processing temperature, interfacial shear stress and compatibility of the polymers, etc. Therefore, apart from the classical mechanical parameters, the interphase created from the interdiffusion should be taken into consideration as an important factor on determining the interfacial instability phenomena. References [1] H. Zhang, K. Lamnawar, A. Maazouz, Rheological modeling of the diffusion process and the interphase of symmetrical bilayers based on PVDF and PMMA with varying molecular weights. Rheol. Acta 51 (2012) 691-711 [2] H. Zhang, K. Lamnawar, A. Maazouz, Rheological modeling of the mutual diffusion and the interphase development for an asymmetrical bilayer based on PMMA and PVDF model compatible polymers, Macromolecules (2012), Doi: http://dx.doi.org/10.1021/ma301620a [3] H. Zhang, K. Lamnawar, A. Maazouz, Role of the interphase in the interfacial flow stability of multilayer coextrusion based on PMMA and PVDF compatible polymers, to be submitted. [4] K. Lamnawar, A. Maazouz, Role of the interphase in the flow stability of reactive coextruded multilayer polymers, Polymer Engineering & Science, 49, (2009), 727 - 739 [5] K. Lamnawar, H. Zhang, A. Maazouz, one chapter” State of the art in co-extrusion of multilayer polymers: experimental and fundamental approaches” in Encyclopedia of Polymer Science and Technology (wiley library) (feature article)

Rheological modeling of carbon nanotube suspensions with rod-rod interactions

AIChE Journal ◽  
2013 ◽  
Vol 60 (4) ◽  
pp. 1476-1487 ◽  
Author(s):  
G. Natale ◽  
M. C. Heuzey ◽  
P. J. Carreau ◽  
G. Ausias ◽  
J. Férec
Keyword(s):  
Carbon Nanotube ◽  
Rheological Modeling

Comparison between electroluminescent organic diodes based on new poly(2,7-fluorene phenylidene) derivatives and commercial polymers

2005 ◽  
Author(s):  
B. Arredondo ◽  
C. Coya ◽  
B. Romero ◽  
A. L. Alvarez ◽  
X. Quintana ◽  
...  
Keyword(s):  
Organic Diodes ◽  
Commercial Polymers

scholarly journals Lagged Ensembles, Forecast Configuration, and Seasonal Predictions

2013 ◽  
Vol 141 (10) ◽  
pp. 3477-3497 ◽  
Author(s):  
Mingyue Chen ◽  
Wanqiu Wang ◽  
Arun Kumar
Keyword(s):  
Lead Time ◽  
Geographical Location ◽  
Seasonal Prediction ◽  
Skill Score ◽  
Negative Influence ◽  
Positive Influence ◽  
Prediction Skill ◽  
Ensemble Size ◽  
Seasonal Forecasts ◽  
Ensemble Forecasts

Abstract An analysis of lagged ensemble seasonal forecasts from the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2), is presented. The focus of the analysis is on the construction of lagged ensemble forecasts with increasing lead time (thus allowing use of larger ensemble sizes) and its influence on seasonal prediction skill. Predictions of seasonal means of sea surface temperature (SST), 200-hPa height (z200), precipitation, and 2-m air temperature (T2m) over land are analyzed. Measures of prediction skill include deterministic (anomaly correlation and mean square error) and probabilistic [rank probability skill score (RPSS)]. The results show that for a fixed lead time, and as one would expect, the skill of seasonal forecast improves as the ensemble size increases, while for a fixed ensemble size the forecast skill decreases as the lead time becomes longer. However, when a forecast is based on a lagged ensemble, there exists an optimal lagged ensemble time (OLET) when positive influence of increasing ensemble size and negative influence due to an increasing lead time result in a maximum in seasonal prediction skill. The OLET is shown to depend on the geographical location and variable. For precipitation and T2m, OLET is relatively longer and skill gain is larger than that for SST and tropical z200. OLET is also dependent on the skill measure with RPSS having the longest OLET. Results of this analysis will be useful in providing guidelines on the design and understanding relative merits for different configuration of seasonal prediction systems.

scholarly journals Forest Pruning Based on Branch Importance

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Xiangkui Jiang ◽  
Chang-an Wu ◽  
Huaping Guo
Keyword(s):  
Decision Tree ◽  
Decision Trees ◽  
Selection Algorithm ◽  
Ensemble Size ◽  
Ensemble Pruning ◽  
Generalization Ability ◽  
Ensemble Selection ◽  
Novel Strategy

A forest is an ensemble with decision trees as members. This paper proposes a novel strategy to pruning forest to enhance ensemble generalization ability and reduce ensemble size. Unlike conventional ensemble pruning approaches, the proposed method tries to evaluate the importance of branches of trees with respect to the whole ensemble using a novel proposed metric called importance gain. The importance of a branch is designed by considering ensemble accuracy and the diversity of ensemble members, and thus the metric reasonably evaluates how much improvement of the ensemble accuracy can be achieved when a branch is pruned. Our experiments show that the proposed method can significantly reduce ensemble size and improve ensemble accuracy, no matter whether ensembles are constructed by a certain algorithm such as bagging or obtained by an ensemble selection algorithm, no matter whether each decision tree is pruned or unpruned.

scholarly journals Kinetic Modelling of Biodegradability Data of Commercial Polymers Obtained under Aerobic Composting Conditions

Eng ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 54-68
Author(s):  
Ilenia Rossetti ◽  
Francesco Conte ◽  
Gianguido Ramis
Keyword(s):  
Kinetic Data ◽  
Kinetic Modelling ◽  
Kinetic Equations ◽  
Second Order ◽  
Aerobic Biodegradation ◽  
First Order ◽  
First Order Kinetics ◽  
Plastic Materials ◽  
Partial Degradation ◽  
Commercial Polymers

Methods to treat kinetic data for the biodegradation of different plastic materials are comparatively discussed. Different samples of commercial formulates were tested for aerobic biodegradation in compost, following the standard ISO14855. Starting from the raw data, the conversion vs. time entries were elaborated using relatively simple kinetic models, such as integrated kinetic equations of zero, first and second order, through the Wilkinson model, or using a Michaelis Menten approach, which was previously reported in the literature. The results were validated against the experimental data and allowed for computation of the time for half degradation of the substrate and, by extrapolation, estimation of the final biodegradation time for all the materials tested. In particular, the Michaelis Menten approach fails in describing all the reported kinetics as well the zeroth- and second-order kinetics. The biodegradation pattern of one sample was described in detail through a simple first-order kinetics. By contrast, other substrates followed a more complex pathway, with rapid partial degradation, subsequently slowing. Therefore, a more conservative kinetic interpolation was needed. The different possible patterns are discussed, with a guide to the application of the most suitable kinetic model.

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