Test particle simulations of resonant interactions between energetic electrons and discrete,multi-frequency artificial whistler waves in the plasmasphere

Modulated high frequency(HF) heating of the ionosphere provides a feasible means of artificially generating extremely low frequency(ELF)/very low frequency(VLF) whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high energy electrons. Combining the ray tracing method and test particle simulations, we evaluate the effects of energetic electron resonant scattering driven by the discrete, multi-frequency artificially generated ELF/VLF waves. The simulation results indicate a stochastic behavior of electrons and a linear profile of pitch angle and kinetic energy variations averaged over all test electrons. These features are similar to those associated with single-frequency waves. The computed local diffusion coefficients show that, although the momentum diffusion of relativistic electrons due to artificial ELF/VLF whistlers with a nominal amplitude of ～ 1 pT is minor, the pitch angle scattering can be notably efficient at low pitch angles near the loss cone, which supports the feasibility of artificial triggering of multi-frequency ELF/VLF whistler waves for the removal of high energy electrons from the magnetosphere. We also investigate the dependences of diffusion coefficients on the frequency interval(△f) of the discrete, multi-frequency waves.We find that there is a threshold value of △f for which the net diffusion coefficient of multi-frequency whistlers is inversely proportional to △f(proportional to the frequency components Nw) when △f is below the threshold value but it remains unchanged with increasing △f when △f is larger than the threshold value. This is explained as being due to the fact that the resonant scattering effect of broadband waves is the sum of the effects of each frequency in the ‘effective frequency band’. Our results suggest that the modulation frequency of HF heating of the ionosphere can be appropriately selected with reasonable frequency intervals so that better performance of controlled precipitation of high energy electrons in the plasmasphere by artificial ELF/VLF whistler waves can be achieved.     

Dynamic investigation of the finite dissolution of silicon particles in aluminum melt with a lower dissolution limit

The finite dissolution model of silicon particles in the aluminum melt is built and calculated by the finite difference method, and the lower dissolution limit of silicon particles in the aluminum melt is proposed and verified by experiments, which could be the origin of microinhomogeneity in aluminum-silicon melts. When the effects of curvature and interface reaction on dissolution are not considered; the dissolution rate first decreases and later increases with time. When the effects of curvature and interface reaction on dissolution are considered, the dissolution rate first decreases and later increases when the interface reaction coefficient （k） is larger than 10 1, and the dissolution rate first decreases and later tends to be constant when k is smaller than 10-3. The dissolution is controlled by both diffusion and interface reaction when k is larger than 10-3, while the dissolution is controlled only by the interface reaction when k is smaller than 10-4.     

Helical Substituted Polyacetylene‐Derived Fluorescent Microparticles Prepared by Precipitation Polymerization

This article reports the first fluorescent microparticles (MPs, approximately 600 nm in diameter) constructed using helical substituted polyacetylene and prepared via a precipitation polymerization approach. The MPs judiciously combine this interesting helical conjugated acetylene, fluorescent material and polymeric particles in one entity. The monomer containing a dansyl group undergoes precipitation polymerization in butanone/n‐heptane mixed solvent, with (nbd)Rh⁺B⁻(C₆H₅)₄ as a catalyst. MPs with a regular morphology are formed in a high yield (>80 wt%). UV‐vis spectroscopy demonstrates that the polymer chains making up the MPs adopt helical structures. The MPs show considerable fluorescence emission (λ_max, 500 nm; excited at 340 nm). Based on SEM and fluorescence images, the formation mechanism of the MPs is proposed. This methodology opens up new ways to prepare functional microstructured materials derived from substituted polyacetylenes, and may also result in opportunities for new practical applications of polyacetylene and its derivatives.

     

Solvent‐Free Fabrication of polyHIPE Microspheres for Controlled Release of Growth Factors

The growth factor bone morphogenetic protein 2 (BMP‐2) is utilized in surgical procedures to improve bone regeneration; however, current treatments deliver BMP‐2 at amounts greater than 100 000 fold of physiological levels, which increases treatment costs and risk of side effects. Drug‐eluting microcarriers developed to improve these therapies have faced significant commercialization challenges including particle size distributions, solvent removal, low encapsulation efficiency, and bioactivity loss. In this study, a solvent‐free method is presented for fabrication of uniform polyHIPE microspheres for controlled growth factor release. Emulsion templating principles and fluid dynamics were used to fabricate uniform particles with tunable particle size (200–800 μm) and pore size (10–30 μm). The ability to independently tune particle and pore size is expected to provide excellent control of release kinetics. Overall, this solvent‐free method for making porous microspheres displays strong promise for the controlled release of BMP‐2 and other growth factors.

     

Visualization of Real‐Time Degradation of pH‐Responsive Polyglycerol Nanogels via Atomic Force Microscopy

Polyglycerol nanogels (nPG) have a huge impact in biomedical applications as drug deliverer due to their high biocompability. For such nPG nanogels, particle degradation is widely used as drug delivery method. The knowledge of this degradation process is limited up to date. In this communication, a real time visualization of such a degradation process is presented for pH‐responsive nPG nanogels via atomic force microscopy (AFM) under ambient and in liquid conditions. The particle height plays a major role in the degradation process and decays exponentially in the beginning of this process. The particle width increases during the process indicating a “decross‐linking” step of the particles into their starting monomers. Measurements under ambient conditions confirm this assumption and provide further insight in the “decross‐linking” step of the nanogels into individual dendritic particles. The present work gives a detailed insight in the particle degradation process, which is essential for further progress for the development of new drug delivery systems.

     

Latest achievements in generalized Lorenz‐Mie theories: A commented reference database

Generalized Lorenz‐Mie theories form a set of analytical approaches dealing with the interaction between electromagnetic arbitrary shaped beams and a class of particles possessing enough symmetries to allow one to use the method of separation of variables. This paper provides a commented reference database concerning generalized Lorenz‐Mie theories for the period 2009‐2013.     

Numerical Simulation of Mixing Characteristics in a Vane Extruder

The polymer vane extruder, whose plasticating and conveying theory is based on elongational rheology, is a significant development in plastic processing equipment. As a result of its unique structure, it is desirable to use numerical simulation to study it. The results can be useful to set process parameters and optimize its structure. In this paper, numerical simulation of the mixing characteristics of the vane extruder was performed with the finite element computational fluid dynamics program POLYFLOW. To visualize the mixing process of the melts in a vane extruder based on the calculation of the transient flow, a particle tracking method was applied. By using the statistical post-processor program POLYSTAT, dispersive mixing and distributive mixing characteristics were evaluated in terms of shear rate, stretching rate, mixing index, and time average mixing efficiency. The simulation results showed that strong stretching existed in the vane extruder demonstrating that the vane extruder generated a more appropriate flow than a common twin-screw extruder to break material particles into smaller ones. The probability functions of mixing efficiency showed that the position near the outflow had the highest mixing efficiency. Furthermore, the time average mixing efficiency of most particles in the vane extruder were larger than that in a twin-screw extruder, indicating that in the vane extruder more mechanical energy was used to generate stretching.     

On aggregate structures in a rod-like haematite particle suspension by means of Brownian dynamics simulations

We have investigated aggregation phenomena in a suspension composed of rod-like haematite particles by means of Brownian dynamics simulations. The magnetic moment of the haematite particles lies normal to the particle axis direction and therefore the present Brownian dynamics method takes into account the spin rotational Brownian motion about the particle axis. We have investigated the influence of the magnetic particle–field and particle–particle interactions, the shear rate and the volumetric fraction of particles on the particle aggregation phenomena. Snapshots of aggregate structures are used for a qualitative discussion and the cluster size distribution, radial distribution function and the orientational correlation functions of the direction of particle axis and magnetic moment are the focus for a quantitative discussion. The significant formation of raft-like clusters is found to occur at a magnetic particle–particle interaction strength much larger than that required for a magnetic spherical particle suspension. This is because the rotational Brownian motion has a significant influence on the formation of clusters in a suspension of rod-like particles with a large aspect ratio. An applied magnetic field enhances the formation of raft-like clusters. A shear flow does not have a significant influence on the internal structure of the clusters, but influences the cluster size distribution of the raft-like clusters.     

Rotating Charged Hairy Black Hole in(2+1) Dimensions and Particle Acceleration

In this paper, we construct rotating charged hairy black hole in(2+1) dimensions for infinitesimal black hole charge and rotation parameters. Then we consider this black hole as particle accelerator and calculate the centerof-mass energy of two colliding test particles near the rotating charged hairy black hole in(2+1) dimensions. As we expected, the center-of-mass energy has infinite value.