The approximation of a well mixed reactor is prevalent when it comes to the modeling of a crystallization process. Since temperature, concentration, and mass content vary due to inhomogeneous mixing, this approximation is a very loose one. The continuously operated seeded tubular crystallizer system developed in our group overcomes obstacles like a slow response to changes in the outer parameters and inhomogeneous mixing. Therefore the applicable well mixed assumption facilitates detailed modeling of the crystallization process by means of population balance equations (PBE) coupled with mass and energy balances. Modeled results were validated by means of experiments. The amount of aggregation events during the crystallization could be quantified and it was proven that the growth of seeded crystals is almost exclusively responsible for solid mass uptake if the reactor is operated appropriately. The performed sensitivity analysis exposed which process settings should be maintained most accurately to avoid fluctuations in the product crystals’ quality attributes and to limit undesired nucleation events. 相似文献
We consider a large, homogeneous portfolio of life or disability annuity policies. The policies are assumed to be independent conditional on an external stochastic process representing the economic–demographic environment. Using a conditional law of large numbers, we establish the connection between claims reserving and risk aggregation for large portfolios. Further, we derive a partial differential equation for moments of present values. Moreover, we show how statistical multi-factor intensity models can be approximated by one-factor models, which allows for solving the PDEs very efficiently. Finally, we give a numerical example where moments of present values of disability annuities are computed using finite-difference methods and Monte Carlo simulations. 相似文献
Like a bamboo rod : Long, bamboo‐like undulated cylinders with distinct branch points and end groups (see picture) were obtained by the stacking of block terpolymer micelles that contain a fluorinated polybutadiene core and a compartmentalized corona of poly(4‐tert‐butoxystyrene) and poly(tert‐butyl methacrylate). Stacking of the polymer micelles, which can be reversed, occurred when the solvent was changed from dioxane to ethanol.
Self-assembly of the 42-amino-acid-long amyloid peptide Aβ1-42 into insoluble fibrillar deposits in the brain is a crucial event in the pathogenesis of Alzheimer's disease. The fibril
deposition occurs through an aggregation process during which transient and metastable oligomeric intermediates are intrinsically
difficult to be accurately monitored and characterised. In this work, the time-dependent Aβ1-42 aggregation pattern is studied by asymmetrical flow field-flow fractionation with on-line multi-angle light scattering detection.
This technique allows separating and obtaining information on the molar mass (Mr) and size distribution of both the early-forming soluble aggregates and the late prefibrillar and fibrillar species, the
latter having very high Mr. Preliminary results demonstrate that unique information on the dynamic aggregation process can be obtained, namely on the
Mr and size of the forming aggregates as well as on their formation kinetics.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
Double Horner–Wadsworth–Emmons reaction of (E)‐2,3‐diaryl‐1,4‐bis(diethylphosphonyl)but‐2‐ene with (p‐substituted) benzaldehydes gave (1E,3E,5E)‐1,3,4,6‐tetraarylhexa‐1,3,5‐trienes in moderate to good yields. Substitution of electron‐withdrawing or ‐donating groups at the para position of the 1,6‐diphenyl groups induced a slight bathochromic shift of UV spectra measured in CHCl3 compared with that of the parent 1,3,4,6‐tetraphenylhexa‐1,3,5‐triene. Although fluorescence was not observed with all the trienes in CHCl3, they markedly emitted visible light in powder forms with quantum yields of 0.15–0.44. Introduction of amino groups at the para position of the 3,4‐diphenyl groups induced a bathochromic shift of emission maxima with good solid‐state quantum yields. Thus, the tetraarylated triene framework is found to serve as a new class of fluorophores that exhibit aggregation‐induced emission. 相似文献
We investigate crossing minimization problems for a set of permutations, where a crossing expresses a disarrangement between elements. The goal is a common permutation π∗ which minimizes the number of crossings. In voting and social science theory this is known as the Kemeny optimal aggregation problem minimizing the Kendall-τ distance. This rank aggregation problem can be phrased as a one-sided two-layer crossing minimization problem for a series of bipartite graphs or for an edge coloured bipartite graph, where crossings are counted only for monochromatic edges. We contribute the max version of the crossing minimization problem, which attempts to minimize the discrimination against any permutation. As our results, we correct the construction from [C. Dwork, R. Kumar, M. Noar, D. Sivakumar, Rank aggregation methods for the Web, Proc. WWW10 (2001) 613-622] and prove the NP-hardness of the common crossing minimization problem for k=4 permutations. Then we establish a 2−2/k-approximation, improving the previous factor of 2. The max version is shown NP-hard for every k≥4, and there is a 2-approximation. Both approximations are optimal, if the common permutation is selected from the given ones. For two permutations crossing minimization is solved by inspecting the drawings, whereas it remains open for three permutations. 相似文献
A DNA‐based covalent versus a non‐covalent approach is demonstrated to control the optical, chirooptical and higher order structures of Nile red ( Nr ) aggregation. Dynamic light scattering and TEM studies revealed that in aqueous media Nr ‐modified 2′‐deoxyuridine aggregates through the co‐operative effect of various non‐covalent interactions including the hydrogen bonding ability of the nucleoside and sugar moieties and the π‐stacking tendency of the highly hydrophobic dye. This results in the formation of optically active nanovesicles. A left‐handed helically twisted H‐type packing of the dye is observed in the bilayer of the vesicle as evidenced from the optical and chirooptical studies. On the other hand, a left‐handed helically twisted J‐type packing in vesicles was obtained from a non‐polar solvent (toluene). Even though the primary stacking interaction of the dye aggregates transformed from H→J while going from aqueous to non‐polar media, the induced supramolecular chirality of the aggregates remained the same (left‐handed). Circular dichroism studies of DNA that contained several synthetically incorporated and covalently attached Nr ‐modified nucleosides revealed the formation of helically stacked H‐aggregates of Nr but—in comparison to the noncovalent aggregates—an inversed chirality (right‐handed). This self‐assembly propensity difference can, in principle, be applied to other hydrophobic dyes and chromophores and thus open a DNA‐based approach to modulate the primary stacking interactions and supramolecular chirality of dye aggregates. 相似文献