Composite binary trees are introduced for an improved kinetic Monte Carlo (kMC) calculation of chemical composition-chain length distributions (CC-CLDs) in polymerization processes, such as the ...bivariate copolymer composition-CLD (CoC-CLD). For the calculation of the CC-CLD, each leaf node of the main tree, which reflects the number of macromolecules with a given chain length, serves as a root node for a sub-tree containing information on the CC distribution for the macromolecules with the selected chain length. For low maximum chain lengths of 1000, the improvement consists already in a reduction of the kMC operations by a factor between 103 and 106. The approach is illustrated for the calculation of the CoC-CLD in free and atom transfer radical copolymerization of methyl methacrylate and styrene while accounting for potential diffusional limitations. Main focus is on the capability of the algorithm to ensure an accurate calculation of the average copolymer composition including high chain lengths.
•Kinetic Monte Carlo modeling of radical polymerization processes.•Introduction of composite binary trees to calculate bivariate distribution.•Modeling of diffusional limitations on the micro-scale.
The Short-Term Ensemble Prediction System (STEPS) is implemented in real-time at the Royal Meteorological Institute (RMI) of Belgium. The main idea behind STEPS is to quantify the forecast ...uncertainty by adding stochastic perturbations to the deterministic Lagrangian extrapolation of radar images. The stochastic perturbations are designed to account for the unpredictable precipitation growth and decay processes and to reproduce the dynamic scaling of precipitation fields, i.e., the observation that large-scale rainfall structures are more persistent and predictable than small-scale convective cells. This paper presents the development, adaptation and verification of the STEPS system for Belgium (STEPS-BE). STEPS-BE provides in real-time 20-member ensemble precipitation nowcasts at 1 km and 5 min resolutions up to 2 h lead time using a 4 C-band radar composite as input. In the context of the PLURISK project, STEPS forecasts were generated to be used as input in sewer system hydraulic models for nowcasting urban inundations in the cities of Ghent and Leuven. Comprehensive forecast verification was performed in order to detect systematic biases over the given urban areas and to analyze the reliability of probabilistic forecasts for a set of case studies in 2013 and 2014. The forecast biases over the cities of Leuven and Ghent were found to be small, which is encouraging for future integration of STEPS nowcasts into the hydraulic models. Probabilistic forecasts of exceeding 0.5 mm h−1 are reliable up to 60–90 min lead time, while the ones of exceeding 5.0 mm h−1 are only reliable up to 30 min. The STEPS ensembles are slightly under-dispersive and represent only 75–90 % of the forecast errors.
The miniemulsion polymerization of styrene mediated by N-(2-methyl-2-propyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (SG1) at 396 K is modeled up to high conversion as a function of the ...targeted chain length (TCL) and particle diameter. Thermal self-initiation and diffusional limitations are explicitly accounted for. The importance of the compartmentalization of nitroxide, initiator and macroradicals and of nitroxide partitioning is assessed using 3-dimensional Smith-Ewart equations. Diffusional limitations on termination are important for higher particle diameters only (>∼70 nm). The influence of diffusional limitations on deactivation, however, can be significant even for intermediate particles diameters (∼40 nm). For a TCL of 300, low particle diameters (<∼20 nm) provide theoretically both a better livingness and control over chain length compared to the bulk case at the expense of a significant reduction of the polymerization rate. For a sufficiently high particle diameter (∼30 nm), a rate acceleration can be obtained accompanied by an improved livingness but with a somewhat reduced control over chain length. For TCLs higher than 300, better overall average polymer properties can be achieved up to particle diameters of ∼ 50 nm. Nitroxide partitioning is shown to lead on average to a limited increase of the polymerization rate without significantly affecting the average polymer properties.
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First-principles density functional theory calculations were performed to obtain detailed insight into the mechanism of benzene hydrogenation over Pt(111). The results indicate that benzene ...hydrogenation follows a Horiuti-Polanyi scheme which involves the consecutive addition of hydrogen adatoms. A first-principles-based reaction path analysis indicates the presence of a dominant reaction path. Hydrogenation occurs preferentially in the meta position of a methylene group. Cyclohexadiene and cyclohexene are expected to be at best minor products, since they are not formed along the dominant reaction path. The only product that can desorb is cyclohexane. Along the dominant reaction path, two categories of activation energies are found: lower barriers at ∼75 kJ/mol for the first three hydrogenation steps, and higher barriers of ∼88 kJ/mol for steps four and six, where hydrogen can only add in the ortho position of two methylene groups. The highest barrier at 104 kJ/mol is calculated for the fifth hydrogenation step, which may potentially be the rate-determining step. The high barrier for this step is likely the result of a rather strong C−H···Pt interaction in the adsorbed reactant state (1,2,3,5-tetrahydrobenzene*) which increases the barrier by ∼15 kJ/mol. Benzene and hydrogen are thought to be the most-abundant reaction intermediates.
The controlled and fast atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAm) initiated by ethyl 2-chloropropionate (ECP) and catalyzed by copper chloride ligated with ...tris(2-dimethylaminoethyl)amine (CuCl·Me6TREN) is reported in water:DMF (1:1 volume based) for a broad range of polymerization conditions (targeted polymerization degree: 50–188; NIPAm0=0.5–2M; T: 10–30°C). For temperatures below 30°C, a faster ATRP is obtained with decreasing temperature, which is explained by the exothermic formation of a pre-reactive complex during propagation. For sufficiently high initial deactivator concentrations (⩾20mol%) a faster ATRP also results, which is proposed to be caused by Lewis acid–base interactions between the Cu(II) species and NIPAm. The kinetic study indicates a limited importance of cyclization reactions implying a limited loss of end-group fidelity. Moreover, for an initial NIPAm concentration of 2M, catalyst disproportionation can be sufficiently suppressed.
The adsorption of 1,3-cyclohexadiene, 1,4-cyclohexadiene, cyclohexene and cyclohexane on Pt(1
1
1) was studied using ab initio density functional theory. For 1,3-cyclohexadiene three adsorption modes ...were distinguished: bridge 1,2-di-σ/3,4-π, hollow 1,4-di-σ/2,3-π and bridge 1,4-di-σ/2,3-π with adsorption energies of −155, −147 and −75
kJ/mol, respectively. Three stable adsorption modes were also identified for 1,4-cyclohexadiene: bridge quadra-σ, hollow di-σ/π and bridge di-π with adsorption energies of −146
kJ/mol, −142
kJ/mol and −88
kJ/mol, respectively. Cyclohexene was found to adsorb in six modes: 4 di-σ and 2 π-adsorption modes. The preferred configuration was found to be boat di-σ with an adsorption energy of −81
kJ/mol. The three other di-σ adsorption modes have comparable adsorption energies, ranging from −64 to −69
kJ/mol. Molecular strain and C
Pt bonding energies are used to elucidate stability trends. Cyclohexane is found to adsorb only at the hollow site whereby the axial hydrogen atoms are positioned over surface Pt-atoms with an adsorption energy of −37
kJ/mol. The calculations correctly predict the weakening of the axial C
H bonds and provide a possible explanation for the large shift in the vibrational frequencies.
Inclusive, comprehensive Stakeholder Identification and Mapping processes are vital for successful environmental management. This is relevant as multi‐disciplinary collaboration becomes increasingly ...popular, and the diversity of people influenced by, or involved in, the management of most projects is greater than ever before. Understanding how relevant parties are analysed in environmental management programmes is required to enable robust and considered methodologies as well as successful, just and equitable outcomes.
The aim of this study was to improve the attribute mapping process, increasing transparency and ensuring representation is both comprehensive and equitable. A rapid scoping review of Scopus and Web of Science was undertaken to collate and analyse peer‐reviewed, published evidence on stakeholder analysis, with a focus on the mapping processes involved in identifying stakeholders and their attributes.
Of the Initial 359 identified papers, 61 were included after three stages of screening. Our results indicate that there is little consistency among practitioners to ensure that Identifying and Mapping Stakeholders is representative: <20% of Case Studies (n = 9) checked the relevancy of their stakeholders after identification. Additionally, definitions at all stages of the stakeholder analysis process were inconsistent across the case studies. Fewer than half of the Case Studies included a definition of Stakeholder (n = 22) or of stakeholder analysis (n = 25).
Capturing a representative sample of relevant parties, without compromising on efficiency, financial or practical constraints, is difficult. Having consistent definitions for the term Stakeholders and stakeholder analysis within environmental management is an important step. Based on the scoping review, we formalise the Analysis process into six stages.
Through the scoping review findings, a decision support tool, MAPTkit (Mapped Attribute Profiling Toolkit) was developed to visualise the heterogeneity and representation of stakeholders across several user‐determined attributes. This tool is non‐prescriptive, drawing attention to potential issues with stakeholder analysis, such as misrepresentation of real‐world stakeholder communities. This ensures engagement across the full range of people to ensure that environmental management projects are multi‐disciplinary and collaborative, while promoting fair and equitable representation.
Attribute profiling of relevant parties is inconsistently defined and applied within environmental management. This scoping review collates examples and methods of stakeholder analysis, and formalises six identification and mapping stages.
Today single event microkinetic (SEMK) models for steam cracking of hydrocarbons allow simulating the conversion of heavy fractions. The key challenge to model the cracking behavior of these heavy ...feedstocks is related to feedstock reconstruction. The latter depends on the required level of molecular detail of the reaction network and of the feedstock characterization/ reconstruction model. This is illustrated for gas condensate feedstocks. Comparison of yield predictions with yields obtained in a pilot plant illustrate how uncertainties in the feedstock characterization propagate to the simulation results. The combination of a SEMK model and the feedstock reconstruction method based on maximization of the Shannon entropy allows to obtain accurate simulation results, provided that the specific density, the global PIONA weight or volume fractions, and the initial, 50% and final boiling point are known. Specifying less commercial indices results in a decrease of the agreement between simulated and experimentally obtained product yields. The developed methodology can be extended in a straight forward way to any heavy feedstock.
Actuellement les modèles cinétiques du vapocraquage des hydrocarbures, par événements constitutifs, permettent de simuler la conversion de fractions lourdes. Le principal défi pour modéliser le craquage de ces matières lourdes est leur reconstruction moléculaire. Celle-ci dépend du niveau de précision moléculaire requis du réseau réactionnel et de la caractérisation/méthode de reconstruction de la charge, comme cela est illustré pour les condensats du gaz naturel par exemple. La comparaison entre les prédictions et les résultats obtenus dans une unité pilote montre comment les incertitudes au niveau de la reconstruction de la charge se propagent au niveau des résultats de la simulation. La combinaison du modèle cinétique par événements constitutifs et de la méthode de reconstruction basée sur la maximisation de l'entropie de Shannon, permet d'obtenir des résultats précis si la densité, la repartition en poids ou en volume des fractions PIONA, et les points d'ébullition initiaux, à 50 % et finals sont connus. Moins il y a d'indices spécifiés, moins il y a de correspondance entre les résultats simulés et ceux obtenus par expérimentation. La méthodologie développée peut être très simplement élargie à d'autres coupes pétrolières.
Context. The influence of binarity on the late stages of stellar evolution remains an open issue. Aims. While the first binary post-AGB stars were serendipitously discovered, the distinct ...characteristics of their spectral energy distribution (SED) allowed us to launch a more systematic search for binaries. We selected post-AGB objects, which exhibit a broad dust excess starting either at H or K, pointing to the presence of a gravitationally bound dusty disc in the system. We initiated an extensive multiwavelength study of those systems and here report on our radial velocity and photometric monitoring results for six stars of early F type, which are pulsators of small amplitude. Methods. To determine the radial velocity of low signal-to-noise ratio time-series data, we constructed dedicated autocorrelation masks based on high signal-to-noise ratio spectra, used in our published chemical studies. The radial velocity variations were analysed in detail to differentiate between pulsational variability and variability caused by orbital motion. When available, the photometric monitoring data were used to complement the time series of radial velocity data and to establish the nature of the pulsation. Finally, orbital minimalisation was performed to constrain the orbital elements. Results. All of the six objects are binaries with orbital periods ranging from 120 to 1800 days. Five systems have non-circular orbits. The mass functions range from 0.004 to 0.57 $M_{\odot}$ and the companions are probably unevolved objects of (very) low initial mass. We argue that these binaries must have evolved through a phase of strong binary interaction when the primary was a cool supergiant. Although the origin of the circumstellar disc is not well understood, the disc is generally believed to have formed during this strong interaction phase. The eccentric orbits of these highly evolved objects remain poorly understood. In one object, the line-of-sight grazes the edge of the puffed-up inner rim of the disc. Conclusions. These results corroborate our earlier statement that evolved objects in binary stars create a Keplerian dusty circumbinary disc. With the measured orbits and mass functions, we conclude that the circumbinary discs seem to have a major impact on the evolution of a significant fraction of binary systems.
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