The 2.5 s Microgravity Drop Tower at National Centre for Combustion Research and Development (NCCRD), Indian Institute of Technology Madras

Space missions involving humans require a better understanding of various phenomena happening in space environments. A number of experiments need to be conducted in microgravity for addressing various issues encompassing safety (primarily fire) and better understanding of fluid and material behaviour. Of the various methods used for obtaining microgravity conditions, drop towers offer ground based microgravity platform. They provide a cost effective platform for doing short duration, repeatable, high quality microgravity experiments. This paper describes key factors that influence the design of a drop tower. The salient features of 2.5 s microgravity tower set up at National Centre for Combustion Research and Development (NCCRD), IIT Madras (IITM) are discussed. Primary features of the three critical elements, namely the drop capsule, the release unit and the decelerator unit are described along with review of these elements in existing drop towers. The IITM drop tower operates in ambient atmospheric conditions to minimise the cost of operation. In order to achieve good quality microgravity levels, a dual capsule configuration is adopted. The shape of the outer capsule is arrived at by detailed transient computational fluid dynamic analysis of the drag shield under free fall condition over the drop height. A pneumatic mechanism is used for capsule release and brought to rest at the end of fall in a carefully designed decelerator unit. The decelerator unit consists of an airbag with controlled air outflow for smooth deceleration.     

Relay selection in mixed RF/FSO system using DF relaying

In this paper, we carry out the performance analysis of relay selection in decode-and-forward (DF)-based mixed radio frequency/free-space optical (RF/FSO) system. We consider two relay selection schemes, namely max-select and distributed switch and stay, and compare their performance with the system having all relays active. The selected DF relay decodes the received RF signal from source and converts it into an optical signal using the subcarrier intensity modulation scheme for transmission over FSO links. The RF links follow generalized \(\eta -\mu \) distribution, while the FSO links are subjected to pointing errors and are assumed to follow gamma–gamma distribution. Novel analytical expressions for cumulative density function and the moment generating function of the equivalent end-to-end signal-to-noise ratio are derived. Capitalizing on the derived statistics, we provide the new closed-form expressions of the outage probability for different relay selection schemes.     

Energy-optimal trajectory planning for car-like robots

When a battery-powered robot needs to operate for a long period of time, optimizing its energy consumption becomes critical. Driving motors are a major source of power consumption for mobile robots. In this paper, we study the problem of finding optimal paths and velocity profiles for car-like robots so as to minimize the energy consumed during motion. We start with an established model for energy consumption of DC motors. We first study the problem of finding the energy optimal velocity profiles, given a path for the robot. We present closed form solutions for the unconstrained case and for the case where there is a bound on maximum velocity. We then study a general problem of finding an energy optimal path along with a velocity profile, given a starting and goal position and orientation for the robot. Along the path, the instantaneous velocity of the robot may be bounded as a function of its turning radius, which in turn affects the energy consumption. Unlike minimum length paths, minimum energy paths may contain circular segments of varying radii. We show how to efficiently construct a graph which generalizes Dubins’ paths by including segments with arbitrary radii. Our algorithm uses the closed-form solution for the optimal velocity profiles as a subroutine to find the minimum energy trajectories, up to a fine discretization. We investigate the structure of energy-optimal paths and highlight instances where these paths deviate from the minimum length Dubins’ curves. In addition, we present a calibration method to find energy model parameters. Finally, we present results from experiments conducted on a custom-built robot for following optimal velocity profiles.     

Machine vision: an aid in reverse Turing test

Information security is perceived as an important and vital aspect for the survival of any business. Preserving user identity and limiting the access of web resources only to the humans and restricting ‘bots’ is an ever challenging area of study. With the increase in computing power and development of newer approaches towards circumvention and reverse-engineering, the recognition gap present between the machines and the humans is said to be decreasing. Turing test and its modified versions are in place to deal with such problems and ways to resolve them by developing complex algorithms for bot prevention systems like CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart). This paper will deal with the use of “Machine Vision” for judging the ability of the machines to compete with humans in breaking sequences of security systems like CAPTCHA. Reverse Turing test will be put to practise here. Complex image recognition technologies and novel approaches towards using Human interactive proofs (HIP) are discussed. The progress of Turing test over the past 60 years has been paid due attention at the end. After all this experimentation, it can be said that the current machine vision is quite poor and is far worse than it is expected to be.     

An 18 megapixel 4.3″ 1443 ppi 120 Hz OLED display for wide field of view high acuity head mounted displays

We developed and fabricated the world's highest resolution (18 megapixel, 1443 ppi) OLED on glass display panel. The design uses a white OLED with color filter structure for high density pixelization and an n‐type LTPS backplane for faster response time than mobile phone displays. A custom high bandwidth driver IC was fabricated. We developed a foveated pixel pipeline appropriate for virtual reality and augmented reality applications, especially mobile systems.     

Scuffing Resistance and Starved Lubrication Behavior in Helicopter Gear Contacts: Dependence on Material,Surface Finish,and Novel Lubricants

A loss of lubrication event within rotorcraft drivetrain components leads to the rapid failure of contacting gear and bearing surfaces, thermal runaway, and catastrophic damage with possible loss of life. This article demonstrates that the scuffing failure of the gear and bearing surfaces can be delayed by varying the properties of the contact materials and residual lubricant in high-speed contacts. A ball-on-disc tribometer is used to simulate loss of lubrication conditions in gears for a variety of material, surface finish, and lubricant combinations to compare relative time to scuffing initiation at high entrainment and sliding velocities (both 16 m/s). Comparisons of material and surface finishing generally show that contacts tend to survive longer without lubricant if the coefficient of friction is relatively low during initial run-in. However, a 9 cSt oil produced longer times to failure than the baseline 5 cSt oil with higher coefficients of friction throughout the experiment. Further measurements showed that silicon nitride and AISI 9310 steel in contact can survive much longer after the lubricant supply is shut off compared to a steel-on-steel contact. The 9 cSt oil, silicon nitride, and superfinished surfaces showed the greatest promise in loss of lubrication technology from these results, with increases of 28, 388, and 1,538%, respectively, over baseline results. Thus, material, surface finish, and novel lubricant selection strategies may allow tailoring of survivability characteristics of aircraft mechanical systems.     

Functional Metal Matrix Composites: Self-lubricating,Self-healing,and Nanocomposites-An Outlook

Many different types of advanced metal matrix composites are now available, some of which possess functional properties. Recent work on particle-reinforced, self-lubricating and self-healing metals and metal matrix nanocomposites (MMNCs) synthesized by solidification synthesis is reviewed. Particle-based MMNCs have been developed by several modern processing tools based on either solid- or liquid-phase synthesis techniques that are claimed to exhibit exciting mechanical properties including improvements of modulus, yield strength, and ultimate tensile strength. This article presents a brief and objective review of the work done over the last decade to identify the challenges and future opportunities in the area of functional nanocomposites. Increasing interest in lightweight materials has resulted in studies on hollow particle-filled metal matrix syntactic foams. Syntactic foams seem especially suitable for development with functional properties such as self-healing and self-lubrication. The metal matrix micro and nanocomposites, and syntactic foams having combinations of ultrahigh strength and wear resistance, self-lubricating, and/or self-healing properties can lead to increased energy efficiency, reliability, comfort of operation, reparability, and safety of vehicles. The focus of the present review is aluminum and magnesium matrix functional materials.     

Compressive Characterization of Single Porous SiC Hollow Particles

Silicon carbide hollow spheres are compression tested to understand their energy absorption characteristics. Two types of particles having tap densities of 440 kg/m³ and 790 kg/m³ (referred to as S1 and S2, respectively) were tested in the present study. The process used to fabricate the hollow spheres leads to porosity in the walls, which affects the mechanical properties of the hollow spheres. The porosity in the walls helps in obtaining mechanical bonding between the matrix material and the particle when such particles are used as fillers in composites. The single-particle compression test results show that the S1 and S2 particles had fracture energies of 0.38 × 10^?3 J and 3.18 × 10^?3 J, respectively. The modulus and fracture energy of the particles were found to increase with increasing diameter. However, the increasing trend shows variations because the wall thickness can vary as an independent parameter. Hollow particle fillers are used in polymer and metal matrices to develop porous composites called syntactic foams. The experimentally measured properties of these particles can be used in theoretical models to design syntactic foams with the desired set of properties for a given application.     

Graphene supported nickel nanoparticle as a viable replacement for platinum in dye sensitized solar cells

A platinum free counter electrode for dye sensitized solar cells was developed using graphene platelets (GP) supported nickel nanoparticles (NPs) as the active catalyst. Few layered GP were prepared by chemical oxidation of graphite powders followed by thermal exfoliation and reduction. The nanoparticles of nickel were deposited directly onto the platelets by pulsed laser ablation. The composite electrodes of GP and Ni nanoparticles (GP-Ni) thus obtained showed better performance compared to conventional Pt thin film electrodes (Std Pt) and unsupported Ni NPs. The efficiencies of the cells fabricated using GP-Ni, Std Pt and Ni NP CEs were 2.19%, 2% and 1.62%, respectively. The GP-Ni composite solar cell operated with an open circuit voltage of 0.7 V and a fill factor of 0.6. Electrochemical impedance spectroscopy using the I(3)(-)/I(-) redox couple confirms lower values of charge transfer resistance for the composite electrodes, 4.67 Ω cm(2) as opposed to 7.73 Ω cm(2) of Std Pt. The better catalytic capability of these composite materials is also reflected in the stronger I(3)(-) reduction peaks in cyclic voltammetry scans.