Quantification of non-isothermal,multi-phase crystallization of isotactic polypropylene: The influence of cooling rate and pressure

The structure of semi-crystalline polymers is strongly influenced by the conditions applied during processing and is of major importance for the final properties of the product. A method is presented to quantify the effect of thermal and pressure history on the isotropic and quiescent crystallization kinetics of four important structures of polypropylene, i.e. the α-, β-, γ- and mesomorphic phase. The approach is based on nucleation and growth of spherulites during non-isothermal solidification, described by the Schneider rate equations combined with the Komogoroff-Avrami expression for space filling. Using an optimization routine the time-resolved multi-phase structure development is accurately described using crystal phase dependent growth rates and an overall nucleation density, all as function of temperature and pressure. It is shown that the maximum growth rate of the α-, and γ-phase increases with applied pressure, while it decreases for the mesomorphic phase. Addition of β-nucleation agent is interpreted as a secondary nucleation density with a coupled β-phase growth. This complete crystallization kinetics characterization of isotactic polypropylene allows prediction of the multi-phase structure development for a wide range of quiescent processing conditions.     

Tubular shaped composites made from polythiophene covalently linked to Prato functionalized N-doped carbon nanotubes

A simple methodology to produce tubular nitrogen-doped carbon nanotube/polythiophene covalently linked composites is described. Nitrogen doped carbon nanotubes (N-CNTs) were made by the floating catalyst CVD method using toluene, ferrocene and tetramethylethylenediamine (TMEDA) as reagents. Functionalization of the N-CNTs was achieved using 3-thiophenecarboxaldehyde and N-methylglycine in 1,2-dichlorobenzene (Prato reaction). Elemental analysis showed nitrogen incorporation of N into the N-CNTs (1.8%) and also the N-methylglycine functionalized N-CNTs (f-N-CNTs; 6.2%). A series of f-N-CNT/thiophene monomer mixtures (weight ratios 1:3, 1:10 and 1:20) were used to make f-N-CNT/polythiophene tubular composites. As the amount of thiophene monomer was increased, the overall diameter of the polymer layer attached onto the N-CNTs increased. Polymer thickness also varied with reaction time (1 h, 12 h and 24 h). The combination of acid functionalization and N–doping gives the best coverage of the CNTs by polythiophene, in which the polythiophene preferentially binds to the f-N-CNTs to give tubular structures.     

Real-time 3D thermal modeling of a magnetically levitated planar actuator

A transient thermal model used to monitor the temperature distribution in real-time in a long-stroke moving-magnet planar actuator is presented. The temperature distribution in the stator coils of the planar actuator depends on the trajectory of the levitated magnet plate as the set of active coils changes with the position of the translator. Using the presented real-time model, the transient thermal behavior can be investigated. Using this thermal model, the commutation algorithm of the planar actuator is adjusted to actively limit the temperature of the coils, and better spread the temperature over the stator coils.     

Optimizing the spatial pattern of networks for monitoring radioactive releases

This study presents a method to optimize the sampling design of environmental monitoring networks in a multi-objective setting. We optimize the permanent network of radiation monitoring stations in the Netherlands and parts of Germany as an example. The optimization method proposed combines minimization of prediction error under routine conditions with maximizing calamity detection capability in emergency cases. To calculate calamity detection capability, an atmospheric dispersion model was used to simulate potentially harmful radioactive releases. For each candidate monitoring network, we determined if the releases were detected within one, two and three hours. Four types of accidents were simulated: small and large nuclear power plant accidents, deliberate radioactive releases using explosive devices, and accidents involving the transport of radioactive materials. Spatial simulated annealing (SSA) was used to search for the optimal monitoring design. SSA was implemented by iteratively moving stations around and accepting all designs that improved a weighted sum of average spatial prediction error and calamity detection capability. Designs that worsened the multi-objective criterion were accepted with a certain probability, which decreased to zero as iterations proceeded. Results were promising and the method should prove useful for assessing the efficacy of environmental monitoring networks designed to monitor both routine and emergency conditions in other applications as well.     

CFD–DEM modelling of particle flow in IsaMills – Comparison between simulations and PEPT measurements

The IsaMill? is a high speed stirred mill with a horizontal configuration that offers advantages such as energy efficiency and an inert grinding environment. A combined computational fluid dynamics (CFD) and discrete element method (DEM) approach was developed to investigate the particle and fluid flows inside a simplified IsaMill?. The configuration of the mill was simpler than that of an actual IsaMill? and no feed flow or rotor was considered. The CFD–DEM model is a progression from earlier DEM only models of “dry” systems which did not account for the fluid phase. The properties of flows at a macroscopically steady state, such as velocity field, distributions of particle velocity and acceleration in the radial direction and power draw, were analysed. Detailed comparisons were carried out between the simulation results and Positron Emission Particle Tracking (PEPT) measurements under similar conditions. The comparisons showed reasonable agreements, confirming that both techniques can capture the key features of the flow. The discrepancies between simulated and measured results were discussed. The findings indicated that the proposed model can be used to generate microdynamic information that is useful in leading to a better understanding of the underpinning physics of flow inside mills.     

New measurement and evaluation of the excitation function of Ni(p,n) reaction for the production of Cu

One of the radioisotopes for which a growing interest exists in nuclear medicine is ⁶⁴Cu. Its branched decay makes it suitable for both diagnostic and therapeutic purposes. Activation cross sections of the proton induced reaction on enriched ⁶⁴Ni have been studied using the stacked foil technique up to 24 MeV. The experimental cross sections are compared with values available from literature. Thick target yields, based on the discrete measured values of the cross sections are calculated and allow a better estimation of the optimum production parameters.     

保存平民记忆的博物馆

要证实哪个国家的博物馆的密度最高是很困难的,因为这在很大程度上取决于所使用的标准。然而,荷兰确实进入了世界前10名的行列。——荷兰博物馆学家彼得·冯·门斯奇