Realizing fragment spawning and fragment growth in the parallelized Discrete Element Method (DEM) during modelling of comminution

The particle based Discrete Element Method (DEM) can be applied to examine comminution processes. In this study, a DEM framework has been extended to model particle breakage without mass loss. After a breakage event occurs, spherical particles, as often considered in the DEM, are replaced by size reduced spherical fragments. During the following time steps, the fragments grow to their desired sizes, so that the mass loss can be counterbalanced. Previously defined overlaps with adjacent unbroken and broken particles (fragments) as well as walls are allowed. The breakage model has been realized in a parallelized DEM framework because comminution processes are often attributed to large numbers of particles and by parallelization the computational time can be reduced efficiently. An oedometer (one-dimensional compression in axial direction of a confined particle bed) has been modelled to investigate the parallelization efficiency and the influence of the permitted overlaps during the growth process on the growth duration. A simplified roller mill has been considered to examine the applicability of the breakage procedure considering parallelization. The results show that parallelization reduces computational time considerably. The breakage procedure is suitable to model comminution processes involving even densely packed particle systems and is superior to existing approaches.     

Multilevel surrogate modeling of an amine scrubbing process for CO2capture

Surrogate models provide a powerful method for simplifying calculations within complex simulations. While surrogate models are broadly applied within chemical engineering, little research exists investigating the level of surrogacy's impact on a simplified process model. In this work, artificial neural networks (ANN) and Kriging models are used as surrogate models at the process, process unit, and thermodynamic levels for a CO₂ amine scrubbing process. The surrogated models are evaluated against an Aspen Plus simulation for accuracy, convergence behavior, computational cost, and ability to extrapolate. The thermodynamic and process unit models can better handle discontinuous, non-smooth behavior, and convergence issues in the surrogated truth model, but poor conditioning in the final system of equations results in a lower accuracy and convergence rate than the process level surrogate. Beyond model accuracy, availability of diverse data, intended re-usability, and the desired outputs must be considered when selecting a level of abstraction.     

Two‐Step Protein Labeling by Using Lipoic Acid Ligase with Norbornene Substrates and Subsequent Inverse‐Electron Demand Diels–Alder Reaction

Inverse‐electron‐demand Diels–Alder cycloaddition (DA_inv) between strained alkenes and tetrazines is a highly bio‐orthogonal reaction that has been applied in the specific labeling of biomolecules. In this work we present a two‐step labeling protocol for the site‐specific labeling of proteins based on attachment of a highly stable norbornene derivative to a specific peptide sequence by using a mutant of the enzyme lipoic acid ligase A (LplA^W37V), followed by the covalent attachment of tetrazine‐modified fluorophores to the norbornene moiety through the bio‐orthogonal DA_inv . We investigated 15 different norbornene derivatives for their selective enzymatic attachment to a 13‐residue lipoic acid acceptor peptide (LAP) by using a standardized HPLC protocol. Finally, we used this two‐step labeling strategy to label proteins in cell lysates in a site‐specific manner and performed cell‐surface labeling on living cells.     

Addition of “Living” Polymers onto C60.

Abstract

Various “living” polymers were grafted onto C₆₀ The number of arms of the so obtained “star” molecules can be controlled by stoechiometry and/or by varying the reactivity of the carbanion on the “living” chain against a double bond on the C₆₀. Even the oxanion of “living” polyethylenoxide is able to add onto the reactive double bonds on C₆₀. In some conditions, the carbanions present on these alkaline salts of grafted fullerenes becomes able to initiate anionic polymerization of vinyl monomers. Using “living” poly(phenylvinylsulfoxide) as a precursor polymer for PA, polyacetylene chains could be attached to the fullerene.     

Macropore formation in p-type silicon: toward the modeling of morphology

The formation of macropores in silicon during electrochemical etching processes has attracted much interest. Experimental evidences indicate that charge transport in silicon and in the electrolyte should realistically be taken into account in order to be able to describe the macropore morphology. However, up to now, none of the existing models has the requested degree of sophistication to reach such a goal. Therefore, we have undertaken the development of a mathematical model (phase-field model) to describe the motion and shape of the silicon/electrolyte interface during anodic dissolution. It is formulated in terms of the fundamental expression for the electrochemical potential and contains terms which describe the process of silicon dissolution during electrochemical attack in a hydrofluoric acid (HF) solution. It should allow us to explore the influence of the physical parameters on the etching process and to obtain the spatial profiles across the interface of various quantities of interest, such as the hole concentration, the current density, or the electrostatic potential. As a first step, we find that this model correctly describes the space charge region formed at the silicon side of the interface.     

Role of transverse temperature gradients in the generation of lamellar eutectic solidification patterns

In directional solidification, a sample is pulled in an externally imposed temperature gradient. When the pulling direction and the temperature gradient are not perfectly aligned, a transverse temperature gradient is generated in the sample. We investigate the dynamics of lamellar eutectic patterns, both by experimental observations and by numerical simulations, and find that it is dramatically affected by a transverse gradient. Whereas, in its absence, the labyrinth patterns that are formed in the initial stage of solidification persist over the entire duration of the experiments, a transverse temperature gradient induces a drift of the pattern which rapidly generates a regular array of lamellae. The drift speed is found to be consistently larger than expected from the normal growth hypothesis, both in simulations and experiments.     

Mechanical Gradient Cues for Guided Cell Motility and Control of Cell Behavior on Uniform Substrates

A novel method for the fabrication and the use of simple uniform poly(dimethylsiloxane) PDMS substrates for controlling cell motility by a mechanical gradient is reported. The substrate is fabricated in PDMS using soft lithography and consists of a soft membrane suspended on top of a patterned PDMS substrate. The difference in the gradient stiffness is related to the underlying pattern. It is shown experimentally that these uniform substrates can modulate the response of cell motility, thus enabling patterning on the surfaces with precise cell motility. Because of the uniformity of the substrate, cells can spread equally and a directional movement to stiffer regions is clearly observed. Varying the geometry underlying the membrane, cell patterning and movement can be quantitatively characterized. This procedure is capable of controlling cell motility with high fidelity over large substrate areas. The most significant advance embodied in this method is that it offers the use of mechanical features to control cell adhesion and not topographical or chemical variations, which has not been reported so far. This modulation of the response of cell motility will be useful for the design and fabrication of advanced planar and 3D biological assemblies suitable for applications in the field of biotechnology and for tissue‐engineering purposes.     

Dependence of the phase separation process on the relative onset of network formation in simultaneous interpenetrating polymer networks

Morphology development during the synthesis at room temperature of an interpenetrating polyurethane/poly(methyl methacrylate) network was investigated by small-angle X-ray scattering in relation with their relative kinetics of formation, determined by Fourier transform infra red spectroscopy. When the time lag between the onset of the two reactions is short, macroscopic phase separation occurs as the polyurethane network is incompletely formed. However, when the time lag increases, the poly(methyl methacrylate) forms into a more continuous network which limits the growth of phase separation to a close environment.     

Behavioral impairments related to cognitive dysfunction in the autoimmune New Zealand black mouse.

Compared the sensorimotor competence and performance of 7–20 mo old male New Zealand Black (NZB) mice and CFW mice on tasks requiring learning and memory, including passive shock avoidance, taste avoidance, tailflick, rotorod, locomotor activity, reflex evaluation, auditory startle response, shock-induced startle response, and active shock avoidance. Results demonstrate that NZBs showed pronounced deficits in performance of passive and active shock avoidance responses. These deficits could not be accounted for by the slight sensorimotor disadvantage of NZBs relative to CFWs. No difference between the 2 mouse strains was seen in passive avoidance behavior at 1.5 mo of age. It is concluded that NZBs display a behavioral deficit related to cognitive dysfunction and that autoimmune mechanisms may be involved in the etiology of this deficit. It is suggested that such behavioral disturbances produced by an autoimmune mechanism may have relevance for the neurological declines observed in aging since the incidence of autoimmune disorders increases markedly in old age. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)