High concentration exfoliation of graphene in ethyl alcohol using block copolymer surfactant and its influence on properties of epoxy nanocomposites

In this work, high concentration exfoliation (～0.2 mg/ml) of graphene in ethyl alcohol is achieved in presence of block copolymer of polyethylene oxide–polypropylene oxide–polyethylene oxide (PEO–PPO–PEO) using sonication followed by centrifugation. The obtained graphene solution is used to prepare epoxy nanocomposites. Flexural tests were conducted over epoxy nanocomposites. The 0.018 wt% of PEO–PPO–PEO block copolymer exfoliated graphene in epoxy matrix shows 21.7% and 15.8% enhancement in flexural modulus and flexural strength respectively as compared to pure epoxy. Transmission electron microscopy reveals well dispersion of graphene in epoxy matrix; and fractography of flexural fractured sample shows graphene dispersion restricts the crack propagation. The well-dispersed graphene in epoxy matrix increase the dielectric constant and thermal stability of epoxy nanocomposites. Further, the enhanced graphene dispersion in epoxy nanocomposites reduces the glass transition temperature (T_g). Thus, enhanced mechanical properties achieved by dispersion of block copolymer exfoliated graphene in epoxy nanocomposites make it suitable for several applications.     

Microstructural Evaluation of NiTi-powder,Steatite, and Steel Balls After Different Milling Conditions

The present research deals with the investigation of morphological characteristics after mechanical alloying of Ni–50 at. %Ti in a high-energy planetary ball mill at various milling times (i.e., 4, 8, 30, 40, 50, and 60 h). Crystallite size was observed to be decreased with the increase of milling time, entire titanium fused in the nickel trellis, and results of intermetallic NiTi. The shape of particle also changed from lamella to globular. Steatite-ceramic and hardened balls were separately used for the ball milling. The observations of morphologies revealed that steatite balls are more durable and wear resistant as compared to steel ball. This research shows that ball milling with steatite-ceramic balls is a cost-effective, high purity, and productive step toward the formation of NiTi intermetallic compound with homogeneous composition and desired particle size.     

Why and when can deep-but not shallow-networks avoid the curse of dimensionality: A review

The paper reviews and extends an emerging body of theoretical results on deep learning including the conditions under which it can be exponentially better than shallow learning. A class of deep convolutional networks represent an important special case of these conditions, though weight sharing is not the main reason for their exponential advantage. Implications of a few key theorems are discussed, together with new results, open problems and conjectures.     

Microstructure evolution of Al-Si-10Mg in direct metal laser sintering using phase-field modeling

Direct metal laser sintering (DMLS) has evolved as a popular technique in additive manufacturing, which produces metallic parts layer-by-layer by the application of laser power. DMLS is a rapid manufacturing process, and the properties of the build material depend on the sintering mechanism as well as the microstructure of the build material. Thus, the prediction of part microstructures during the process may be a key factor for process optimization. In addition, the process parameters play a crucial role in the microstructure evolution, and need to be controlled effectively. In this study, the microstructure evolution of Al-Si-10Mg alloy in DMLS process is studied with the help of the phase field modeling. A MATLAB code is used to solve the phase field equations, where the simulation parameters include temperature gradient, laser power and scan speed. From the simulation result, it is found that the temperature gradient plays a significant role in the evolution of microstructure with different process parameters. In a single-seed simulation, the growth of the dendritic structure increases with the increase in the temperature gradient. When considering multiple seeds, the increasing in temperature gradients leads to the formation of finer dendrites; however, with increasing time, the dendrites join and grain growth are seen to be controlled at the interface. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0213-1     

An array of microactuated microelectrodes for monitoring single-neuronal activity in rodents

Arrays of microelectrodes used for monitoring single- and multi-neuronal action potentials often fail to record from the same population of neurons over a period of time for several technical and biological reasons. We report here a novel Neural Probe chip with a 3-channel microactuated microelectrode array that will enable precise repositioning of the individual microelectrodes within the brain tissue after implantation. Thermal microactuators and associated microelectrodes in the Neural Probe chip are microfabricated using the Sandia's Ultraplanar Multi-level MEMS Technology (SUMMiTV) process, a 5-layer polysilicon micromachining technology of the Sandia National labs, Albuquerque, NM. The Neural Probe chip enables precise bi-directional positioning of the microelectrodes in the brain with a step resolution in the order of 8.8 microm. The thermal microactuators allow for a linear translation of the microelectrodes of up to 5 mm in either direction making it suitable for positioning microelectrodes in deep structures of a rodent brain. The overall translation in either direction was reduced to approximately 2 mm after insulation of the microelectrodes with epoxy for monitoring multi-unit activity. Single unit recordings were obtained from the somatosensory cortex of adult rats over a period of three days demonstrating the feasibility of this technology. Further optimization of the microelectrode insulation and chip packaging will be necessary before this technology can be validated in chronic experiments.     

Hydrogen production from water: Summary of recent research and development presented at the Fifth WHEC

About 44% of the R & D papers presented at the 5th World Hydrogen Energy Conference (from 15 to 19 July 1984, Toronto, Canada) were concerned with methods of hydrogen production from water. Both traditional and innovative technologies for water electrolysis were reviewed in detail at this conference. The main installations of water electrolysis were introduced. Thermochemical methods of water decomposition, which were flourishing at the 1st and 2nd WHECs, have declined in emphasis since then. Thirteen papers were presented on the thermochemical method, but no radical improvements were described. Photolytic methods of water decomposition, and especially photoassisted electrolysis using semiconductor electrodes, have proved to be one of the most popular areas of research, beginning about ten years ago. Theoretical treatment, as well as efficiency limits, were discussed in detail, but inexpensive, appropriate electrode materials, with better solar efficiencies than TiO₂, although sharing its chemical stability, were not reported.