Gravity Drawing of Micro‐ and Nanofibers for Additive Manufacturing of Well‐Organized 3D‐Nanostructured Scaffolds

This work introduces a gravity fiber drawing (GFD) method of making single filament nanofibers from polymer solutions and precise alignment of the fibers in 3D scaffolds. This method is advantageous for nanofiber 3D alignment in contrast to other known methods. GFD provides a technology for the fabrication of freestanding filament nanofibers of well‐controlled diameter, draw ratio, and 3D organization with controllable spacing and angular orientation between nanofibers. The GFD method is capable of fabricating complex 3D scaffolds combining fibers with different diameters, chemical compositions, mechanical properties, angular orientations, and multilayer structures in the same construct. The scaffold porosity can be as high as 99% to secure transport of nutrients and space for cell infiltration and differentiation in tissue engineering and 3D cell culture applications.     

Networks of materials: Construction and structural analysis

Modeling and analysis of the materials universe is an emerging area of research with many important applications in materials science. The main goal is to create a map of materials which allows not only to visualize and navigate the materials space, but also reveal complex relationships and “connections” among materials and potentially find clusters of materials with similar properties. In this paper, we consider the problem of mapping and exploring the materials universe using network science tools and concepts. The networks are based on the open-source materials data repository AFLOW.org where each material is represented as a node, and each pair of nodes is connected by a link if the respective materials exhibit a high level of similarity between their Density of States (DOS) functions. We discuss the importance of similarity measure selection, investigate basic structural properties of the resulting networks, and demonstrate advantages and limitations of the proposed approaches. Materials networks, similarity measures, DOS function, materials informatics, network analysis, clique.     

Correlation between the performance and microstructure of Ti/Al/Ti/Au Ohmic contacts to p-type silicon nanowires

Understanding the electrical and microstructural aspects of contact formation at nanoscale is essential for the realization of low-resistance metallization suitable for the next generation of nanowire based devices. In this study, we present detailed electrical and microstructural characteristics of Ti/Al/Ti/Au metal contacts to p-type Si nanowires (SiNWs) annealed at various temperatures. Focused ion beam cross-sectioning techniques and scanning transmission electron microscopy (STEM) were used to determine the microstructure of the source/drain metal contacts of working SiNW field-effect transistors (FETs) annealed for 30 s in the 450-850?°C temperature range in inert atmosphere. Formation of titanium silicides is observed at the metal/semiconductor interface after the 750?°C anneal. Extensive Si out-diffusion from the nanowire after the 750?°C anneal led to Kirkendall void formation. Annealing at 850?°C led to almost complete out-diffusion of Si from the nanowire core. Devices with 550?°C annealed contacts had linear electrical characteristics; whereas the devices annealed at 750?°C had the best characteristics in terms of linearity, symmetric behavior, and yield. Devices annealed at 850?°C had poor yield, which can be directly attributed to the microstructure of the contact region observed in STEM.     

Experimental study of hydrodynamics and thermal behavior of a pseudo‐2D spout‐fluidized bed with liquid injection

A novel nonintrusive technique is presented to investigate hydrodynamic and thermal behavior of gas–solid spout‐fluidized beds with liquid injection, by simultaneously capturing visual and infrared images. Experiments were performed in a pseudo‐2D bed with draft plates filled with glass or γ‐alumina particles to investigate the effect of liquid injection and particle properties on the flow characteristics. For the glass particles under dry and wet conditions, time‐averaged particle velocities show similar quasi‐steady‐state behavior. However, under wet conditions, lower particle velocities were observed in both spout and annulus as compared with the dry system. Whereas, γ‐alumina particles do not show considerable variation in the particle velocities under dry and wet conditions and fluidize well at higher liquid injection rates. Additionally, for the glass particles, the particle temperature significantly decreases as compared to the γ‐alumina particles. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1146–1159, 2015     

Network-based optimization techniques for wind farm location decisions

This study aims to find appropriate locations for wind farms that can maximize the overall energy output while controlling the effects of wind speed variability. High wind speeds are required to obtain the maximum possible power output of a wind farm. However, balancing the wind energy supplies over time by selecting diverse locations is necessary. These issues are addressed using network-based models. Hence, actual wind speed data are utilized to demonstrate the advantages of the proposed approach.     

Structure-mechanical properties correlation in bulk LiPON glass produced by nitridation of metaphosphate melts

The glassy solid electrolyte Lithium phosphorous oxynitride (LiPON) has been widely researched in thin film solid state battery format due to its outstanding stability when cycled against lithium. In addition, recent reports show thin film LiPON having interesting mechanical behaviors, especially its ability to resist micro-scale cracking via densification and shear flow. In the present study, we have produced bulk LiPON glasses with varying nitrogen contents by ammonolysis of LiPO₃ melts. The resulting compositions were determined to be LiPO_3-3z/2N_z, where 0 ≤ z ≤ 0.75, and the z value of 0.75 is among the highest ever reported for this series of LiPON glasses. The short-range order structures of the different resulting compositions were characterized by infrared, Raman, ³¹P magic angle spinning nuclear magnetic resonance, and X-ray photoelectron spectroscopies. Instrumented nano-indentation was used to measure mechanical properties. It was observed that similar to previous studies, both trigonally coordinated (N_t) and doubly bonded (N_d) N co-exist in the glasses in about the same amounts for z ≤ 0.36, the limit of N content in most previous studies. For glasses with z > 0.36, it was found that the fraction of the N_t increased significantly while the fraction of N_d correspondingly decreased. The incorporation of nitrogen increased both the elastic modulus and hardness of the glass by approximately a factor of 1.5 when N/P ratio reaches 0.75. At the same time, an apparent embrittlement of the glass was observed due to nitridation, which was revealed by nanoindentation with an extra sharp nanoindenter tip.     

CFD-DEM Simulation of Superquadric Cylindrical Particles in a Spouted Bed and a Rotor Granulator

The fluidization behavior of cylindrical particles in a spouted bed was first investigated experimentally using a camera setup. The obtained average spouted bed height was used to evaluate the accuracy of different drag models in CFD-DEM simulations with the superquadric approach to model the particle shape. The drag model according to Sanjeevi et al. showed the best agreement. With this model, cylindrical particles were simulated in a rotor granulator and the particle dynamics were compared with the fluidization of volume equivalent spherical particles.