Golden angle‐inspired design of massive MIMO tapered slot array with less correlation for 5G lower band applications

In this article, for the first time, we come up with a nature‐inspired MIMO antenna configuration that could provide less correlated wireless channels for 5G lower band (3000‐4200 MHz). Essentially, the cross‐correlation among the antenna elements is reduced by incorporating the concept of golden angle into a cylindrical configuration of tapered slot antenna array. The golden angle helps in arranging the end‐fire radiating tapered slot antennas (TSAs) in such a way that there will not be any spatial overlap among the radiation fields of the individual antenna elements. The idea is validated with 24 TSA elements placed in a cylindrical fashion. The envelope correlation coefficient (ECC) is calculated from the simulations in ANSYS HFSS and verified with measurements. The ECC value is found to be less than 0.01 in the range of 3 GHz to 4.25 GHz. The impedance matching and mutual coupling between the elements are found to be very good in the above‐mentioned frequency range from the simulations and measurements. It is believed that the application of golden angle concept to MIMO antennas would open up the windows for implementation of dense massive MIMO.     

Synthesis of nitrogen‐doped graphene catalyst by high‐energy wet ball milling for electrochemical systems

Platinum group metal‐based (PGM) catalysts are widely applied in many electrochemical systems such as fuel cells or metal–air batteries because of their excellent catalytic performance. But the high raw material cost of PGM catalysts has become a significant issue. In recent years, huge efforts have been made to reduce the material cost of electrochemical systems by developing non‐PGM catalysts, and as one of the promising non‐PGM catalysts, nitrogen‐doped graphene (N‐G) has emerged. In this research, nanoscale high‐energy wet ball milling methodology was investigated as an effective synthesis method for N‐G catalysts by using graphene oxide and melamine as raw materials. The main purpose is to study reaction mechanism of the synthesis process and the physical, chemical, and electrochemical properties of N‐G catalysts generated by this mechanochemical approach. The elemental composition, chemical bonding composition, and electron transfer number of the synthesized products were characterized. The results show that the electron transfer number of the N‐G catalyst with 23.2 at% nitrogen doping content, synthesized by the high‐energy wet ball milling method, has attained a value of 3.87, which is close to the number (3.95) of Pt/C catalysts, and the grinding time was found to be a significant factor in the properties of N‐G catalysts in the experiments. The results also show that the high‐energy wet ball milling developed in this research is a promising method to synthesize high‐performance N‐G catalysts with a simple and easy controllable approach. Copyright © 2016 John Wiley & Sons, Ltd.     

One-dimensional turbulence simulations of hydrogen-fueled HCCI combustion

Homogeneous charge compression ignition (HCCI) engines fueled by hydrogen have the potential to provide cost-effective power with high efficiencies and very low emissions. This paper investigates the ability of two of the most commonly used injection methods, port fuel injection (PFI) and single-pulse direct injection (DI), to prepare an ideal in-cylinder hydrogen-air mixture and control the autoignition process. Computations are performed using the one-dimensional turbulence (ODT) model formulated for engine simulations. It is found that direct injection is able to prepare a more uniformly lean mixture and control the autoignition more effectively than port fuel injection. A combination of ignition modes are found to be operating when PFI is used as compared to mainly volumetric autoignition in the case of DI. Also, DI is able to maintain comparatively lower temperatures than PFI.     

Obtaining medial responses from steerable filters

In building up a multiscale, medial axis representation, the generation of medial responses from a set of boundary responses at multiple scales can be a computationally intensive process. Polar separable medial weighting kernels are applied to the computation of medial responses. An approximate method for the synthesis of rotated kernels is proposed. Because of the need to not only rotate, but to displace boundary responses by an amount dependent on the image scale, the traditional steerable filter approach must be modified to yield correct medial responses. Comparisons between integral evaluation and the adaptive filtering approximations show that 100-fold increases in modestly sized images at a single scale are possible. The error in the approximation is insignificant     

Reduced order models for diffusion systems

Mathematical models for diffusion processes like heat propagation, dispersion of pollutants, etc. are normally partial differential equations which involve certain unknown parameters. To use these mathematical models as substitutes of the true system, one has to determine these parameters. Partial differential equations (PDE) of the form u ( x, t ) / t = Lu ( x, t ) (1) where L is a linear differential (spatial) operator, describe infinite dimensional dynamical systems. To compute a numerical solution for such partial differential equations, one has to approximate the underlying system by a finite order one. By using this finite order approximation, one then computes an approximate numerical solution for the PDE. Here, we consider a simple case of heat propagation in a homogeneous wall. The resulting partial differential equation, which is of the form (1), normally involves some unknown parameters. To estimate these unknown parameters, one has to approximate the infinite order model by a finite order model. For this purpose, we construct some finite order models by using certain existing numerical techniques like Galerkin and Collocation, etc. And, later, depending on their merit one chooses a suitable approximation for estimating the unknown parameters. In this paper we concentrate only on the model reduction aspects of the problem and not on the parameter estimation part. In particular, we examine the model order reduction capabilities of the Chebyshev polynomial methods used for solving partial diferential equations.     

CHITRA: Cognitive handprinted input-trained recursively analyzing system for recognition of alphanumeric characters

A novel system for recognition of handprinted alphanumeric characters has been developed and tested. The system can be employed for recognition of either the alphabet or the numeral by contextually switching on to the corresponding branch of the recognition algorithm. The two major components of the system are the multistage feature extractor and the decision logic tree-type catagorizer. The importance of good features over sophistication in the classification procedures was recognized, and the feature extractor is designed to extract features based on a variety of topological, morphological and similar properties. An information feedback path is provided between the decision logic and the feature extractor units to facilitate an interleaved or recursive mode of operation. This ensures that only those features essential to the recognition of a particular sample are extracted each time. Test implementation has demonstrated the reliability of the system in recognizing a variety of handprinted alphanumeric characters with close to 100% accuracy.Most of this work was carried out at the School of Automation, Indian Institute of Science, Bangalore, India.     

Multi-walled carbon nanotube growth on oxidized silicon substrates using cyclohexane precursor by chemical vapor deposition

Randomly oriented multi-walled nanotubes (MWNTs) are grown by a thermal chemical vapor deposition (CVD) process from cyclohexane precursor on a 20% copper-80% nickel (Cu-Ni) catalyst on oxidized silicon substrates. This combination of precursor and catalyst, to our knowledge, has been employed for the first time to demonstrate growth of multi-walled carbon nanotubes. The effects of annealing, gas ambient and catalyst layer thickness on the morphology of the grown carbon layers are discussed. The low resistivity values of the MWNTs grown on oxidized silicon substrates are attractive for their potential use in photonic devices and display applications.     

An overview of feed-forward design techniques for high-gain wideband operational transconductance amplifiers

In this paper, feed-forward techniques are revised and used for the design of high-frequency operational transconductance amplifiers (OTA). For the same power consumption and similar transistor dimensions, the two- and three-path folded-cascode OTA's present both smaller settling error and faster response as compared to the typical folded-cascode topology.Also, a no-capacitor feed-forward (NCFF) compensation which uses a high-frequency pole-zero doublet to obtain high gain, high GBW and a good phase margin is discussed. The settling-time of the NCFF topology can be faster than that of OTA's with Miller compensation, even if the latter topology uses larger transconductance values. Experimental results for the multi-trajectory OTA's fabricated in the AMI 0.5 μm CMOS process demonstrate the feasibility of the feed-forward schemes.