On the axial propagation of kink bands in fiber composites : Part ii analysis

A new micromechanical model is presented to simulate the steady-state axial propagation of kink bands investigated experimentally in the accompanying paper (Part I) . The fibers are in a hexagonal array and are assumed to be isotropic and linearly elastic, while the matrix is modeled as an elastic-powerlaw viscoplastic solid. Matrix properties for the model are determined from shear tests on the composite and compression tests on neat PEEK. The model is used to predict the propagation stress (σ_P) of the AS4⧹PEEK composite and to investigate the sensitivity of σ_P to band inclination, matrix properties, and loading rate. A simple model recently reported in the literature is calibrated to the current material system and compared with the present experimental data and model predictions. The micromechanical model is found to predict the propagation stress reasonably well and to capture the rate dependence of the composite. The simple model is found to capture the trends of the behavior.     

Kinetic study of complicated anti-solvent and cooling crystallization of disodium 5′-ribonucleotide

Disodium 5′-ribonucleotide, which is composed of disodium 5′-inosine (IMP) and disodium 5′-guanosine (GMP), is an important food additive. The lack of kinetic studies of it causes a lack of clarity in understanding the complicated multi-solute crystallization of IMP + GMP in ethanol-water. In this work, process analytical technology tools were used to obtain the thermodynamics and kinetic data from the experiments, the kinetic parameters of anti-solvent and cooling crystallization were investigated. The crystal form of IMP + GMP mixed crystal was determined, which was consistent with the IMP whether crystallized from pure water or ethanol-water. The effects of different anti-solvent addition rates and cooling rates on the metastable zone widths were studied, and the opposite effect on metastable zone width was found. The modified exponential empirical function was developed to correlate nucleation and growth kinetic equations under different conditions. The kinetic data were well fitted with adjusted correlation coefficient (adj-R² > 0.7), which is sufficient to provide a valid reference for process design and control.     

Computational fluid dynamics simulations of aerosol behavior in a high-speed (Heubach) rotating drum dustiness tester

Potential exposure from hazardous dust may be assessed by evaluating the dustiness of the powders being handled. Dustiness is the tendency of a powder to aerosolize with a given input of energy. Previously we used computational fluid dynamics (CFD) to numerically investigate the flow inside the European Standard (EN15051) rotating drum dustiness tester during its operation. The present work extends those CFD studies to the widely used Heubach rotating drum. Air flow characteristics are investigated within the Abe-Kondoh-Nagano k-epsilon turbulence model; the aerosol is incorporated via a Euler-Lagrangian multiphase approach. The air flow inside these drums consists of a well-defined axial jet penetrating relatively quiescent air. The spreading of the Heubach jet results in a fraction of the jet recirculating as back-flow along the drum walls; at high rotation rates, the axial jet becomes unstable. This flow behavior qualitatively differs from the stable EN15051 flow pattern. The aerodynamic instability promotes efficient mixing within the Heubach drum, resulting in higher particle capture efficiencies for particle sizes d < 80 μm.     

A state-of-the-art review on transition between the fast fluidization and pneumatic transport of Geldart group B particles

The fluidization state in the circulating fluidized bed (CFB) boiler is crucial to its stable and safe operation. However, up to now, the research field has not reached unanimity on whether the fluidization regime that the upper furnace of the boiler operates in is the fast fluidization or pneumatic transport. To this end, this paper reviewed relevant research on the transition between the fast fluidization and pneumatic transport of Geldart group B particles, including the flow characteristics of the fast fluidization, the transition condition between the fast fluidization and pneumatic transport, the determination methods of the transport velocity u_tr and saturation carrying capacity G_s1 and the influencing factors on these two parameters. Previous research findings can provide certain guidelines for the design and optimization of the CFB boiler, and result in plenty of prediction correlations for u_tr and G_s1. Nonetheless, owing to insufficient data available on Geldart group B particles, especially the ones obtained under high temperature or pressure conditions and in large-scale CFB apparatuses, the existing correlations are not well suited for the prediction of u_tr and G_s1 of Geldart group B particles. Thus, further efforts are urgently demanded on the fast fluidization transition of Geldart group B particles.     

Si-induced insertion of Li into SiC to form Li-rich SiC twin crystal

The energy density of Li-ion batteries is closely related to the capacity and average voltage of cathode materials. Unfortunately, current cathode materials either have low capacity or voltage, which limits the development of high-energy-density Li-ion batteries. This has given challenge to many attempts to develop new cathode materials with high capacity and voltage. In this study, we find that Li easily inserts into the (111) plane of SiC in the presence of Si, and a well-organized Li-rich SiC twin crystal is formed. Ultraviolet–visible diffuse reflectance spectra and electrochemical test results suggest that this Li-rich SiC twin crystal possesses the band gap energy of 3.5 eV and charging capacity of 1979 mAh/g at the current density of 200 mA/g, making it a promising candidate for the cathode material in high-capacity Li-ion batteries. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy results reveal that Si-induced Li insertion contributes to the changes in the surface species and structure of pristine SiC. These findings suggest that the Li-rich SiC twin crystal raises new possibilities for the development of high-capacity cathode materials and merits further investigation to expand its application scope.     

Bayesian Analysis for Quantitative NMR Flow and Diffusion Imaging

This study demonstrates the use of a Bayesian statistical method for data analysis in practical flow and diffusion measurements based on pulsed-held-gradient magnetic-resonance imaging. In addition to providing estimates of both the velocity and the diffusion coefficient at each voxel, the technique produces reliable fitting errors for these measurements. Bayesian analysis is especially useful, compared to the Fourier transform method, for treating noisy data which are truncated and/or sparsely and nonuniformly sampled in q, the wavevector for motion encoding. Nonuniform sampling in q is shown to be more efficient than uniform sampling for velocity and diffusion measurement; it can result in smaller fitting errors for the estimated parameters corresponding to fewer q samples and hence less data-acquisition time. The specific example of laminar flow of water in a straight cylindrical tube is illustrated with experimental and simulated data.     

Interfacial self-assembly growth of mesoporous polydopamine nanofilms for formaldehyde sensing

Mesoporous polymer nanofilms combine the advantages of the unique structure of mesopores, the quasi-2D configuration of the films, and the inherent properties of polymers, and have become a kind of ideal candidate for the high-performance micro-nano devices due to their highly accessible surface area and exposed active sites. However, the facile preparation of polymer nanofilms with well-defined mesostructures has remained a great challenge due to the lack of synthetic strategies. In this study, we developed a simple soft-template interfacial co-assembly strategy to in-situ construct mesoporous polydopamine nanofilms with uniform thickness (30 nm) and regularly distributed mesopore arrays (average pore size of 12 nm) on surfaces with different types and morphologies. Furthermore, a single-layer mesoporous polymer nanofilm was directly grown on a quartz crystal microbalance substrate and its performance for sensing formaldehyde was studied. The resulted sensor showed excellent sensing response, fast response/recovery dynamics, and great stability, presenting a great promising landscape for trace detection of formaldehyde gas.     

BEEM studies on GaAs/AlxGa1–xAs quantum wire structures

Ballistic electron emission microscopy (BEEM) was used to study laterally patterned GaAs/Al_xGa_1–xAs heterostructures. The measurements were carried out at room temperature in air as well as in liquid helium. Wet chemically etched quantum wires were identified both in topographic and BEEM current imaging. We find that the BEEM current is enhanced if ballistic electronis are injected directly into the quantum wire. The subsurface Al_xGa_1–xAs barrier influences the collector current by determining the BEEM current threshold and by influencing the Fermi level pinning position.