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.     

Design Optimization of EDFA for 16 × 10 Gbps Data Rate DWDM System Using Different Pumping Configurations

Wireless Personal Communications - In this paper, the erbium doped fiber amplifier (EDFA) is used as a booster and a pre amplifier in the dense wavelength division multiplexing system. We optimize...     

Numerical simulations of partially‐filled rubber mixing in a 2‐wing rotor‐equipped chamber

Partially filled internal batch mixers are used for mixing of rubber compounds in the polymer industry. The use of mixing in such mixers equipped with a rotor is critical to the process itself, and hence, understanding of mixing is important in terms of evaluating how various operating parameters such as rpm, fill factor, and ram pressure affect distribution and dispersion of materials. The objective of the current study is to gain valuable insights on the influence of fill factor, which is the volume of the material relative to the volume of the chamber. Two‐dimensional (2D) computational fluid dynamics (CFD) simulations of rubber mixing in a 2‐wing rotor‐equipped chamber are presented here, for the first time, for fully‐filled/100% and partially‐filled/75% chambers. The volume‐of‐fluid (VOF) technique is employed to capture the interface between the rubber and air in partially filled isothermal simulations. Flow patterns are visualized to analyze the material movement. Massless particles are injected and various statistics are calculated from their positions in order to compare dispersive and distributive mixing characteristics between the fully‐filled and partially‐filled cases. Specifically, quantities such as mixing index and the maximum shear stress distribution history of particles are analyzed to obtain information about dispersive mixing, while length of stretch and cluster distribution index, also calculated from particles, are presented to investigate distributive mixing capabilities. All the results consistently demonstrated the superior effectiveness of partially‐filled mixing chambers in terms of their dispersive and distributive mixing characteristics in comparison to fully‐filled chambers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44250.     

Non‐normality can facilitate pulsing in biomolecular circuits

Non‐normality can underlie pulse dynamics in many engineering contexts. However, its role in pulses generated in biomolecular contexts is generally unclear. Here, the authors address this issue using the mathematical tools of linear algebra and systems theory on simple computational models of biomolecular circuits. They find that non‐normality is present in standard models of feedforward loops. They used a generalised framework and pseudospectrum analysis to identify non‐normality in larger biomolecular circuit models, finding that it correlates well with pulsing dynamics. Finally, they illustrate how these methods can be used to provide analytical support to numerical screens for pulsing dynamics as well as provide guidelines for design.Inspec keywords: linear algebra, feedforward, eigenvalues and eigenfunctions, network analysis, molecular biophysicsOther keywords: nonnormality, biomolecular circuits, pulse dynamics, engineering contexts, biomolecular contexts, linear algebra, systems theory, simple computational models, standard models, larger biomolecular circuit models     

Facile Synthesis of “Quench‐Free Glass” and Ceramic‐Glass Composite for LTCC Applications

The 10 mol% ZnO–2 mol% B₂O₃–8 mol% P₂O₅–80 mol% TeO₂ (ZBPT) glass was prepared by quenching as well as slowly cooling the melt. The ZBPT glass prepared by both methods show similar microwave dielectric properties. ZBPT glass has an ε_r of 22.5 (at 7 GHz), Q_u × f of 1500 GHz, and τ_f of ?100 ppm/°C. The ceramic‐glass composites of Sr₂ZnTeO₆ (SZT) and ZBPT is prepared through two convenient methods: (a) conventional way of co‐firing the ceramic with ZBPT glass powder and (b) a nonconventional facile route by co‐firing the ceramic with precursor oxide mixture of ZBPT glass at 950°C. In the former route, SZT + 5 wt% ZBPT composite sintered at 950°C showed moderately good microwave dielectric properties (ε_r = 13.4, Q_u × f = 4500 GHz and τ_f = ?52 ppm/°C). Although the SZT + 5 wt% ZBPT composite prepared through the nonconventional method also showed similar microwave dielectric properties (ε_r = 13.8, Q_u × f = 5300 GHz and τ_f = ?50 ppm/°C), the synthesis procedure is much simplified in the latter case. The composites are found to be chemically compatible with Ag. The composite containing 5 wt% ZBPT prepared through conventional and nonconventional ways shows linear coefficients of thermal expansion of 7.0 ppm/°C and 7.1 ppm/°C, respectively. Both the composites have a room‐temperature thermal conductivity of 2.1 Wm^?1 K^?1.     

Application of fly ash on the growth performance and translocation of toxic heavy metals within Cajanus cajan L.: Implication for safe utilization of fly ash for agricultural production

The present study was undertaken to examine the influence of the application of fly ash (FA) into garden soil for Cajanus cajan L. cultivation and on accumulation and translocation of hazardous metals from FA to edible part. Numerous studies have been reported on the growth and yield of agricultural crops under FA stress; however, there is a dearth of studies recommending the safe utilization of fly ash for crop production. Pot experiments were conducted on C. cajan L., a widely cultivating legume in India for its highly nutritious seeds. C. cajan L. were grown in garden soil and amended with varying concentrations of FA in a weight/weight ratio (0%, 25%, 50% and 100%; w/w). Incorporation of fly ash from 25% to 100% in garden soil increases the levels of pH, particle density, porosity and water holding capacity from 3.47% to 26.39%, 3.98% to 26.14%, 37.50% to 147.92% and 163.16% to 318.42%, respectively, than the control while bulk density decrease respectively from 8.94% to 48.89%. Pot experiment found that accumulation and translocation of heavy metals in tested plant depends on the concentration of FA. Addition of FA at lower concentration (25%) had shown positive results in most of the studied parameters of growth and yield (14.23% than control). The experimental results confirmed that lower concentration of FA (25%) is safe for C. cajan cultivation, which not only enhanced the yield of C. cajan L. significantly but also ensured the translocation of heavy metals to edible parts within the critical limits.     

Phase formation between La(Sr)Ga(Mg)O3 and Ce(La)O2 for solid oxide fuel cell applications

In strontium- and magnesium-doped LaGaO₃ (LSGM) electrolyte-based solid oxide fuel cells (SOFC), lanthanum-doped CeO₂ (LDC) is usually used as buffer layer material to prevent reactions between LSGM electrolyte and NiO-based anode. In literature, based on results for one particular LSGM composition, a fixed buffer layer composition of 40% La-doped ceria (LDC40) has been used even with electrolytes of different LSGM compositions. In this study, we report the results of a comprehensive study of phase formations between various LSGM and LDC compositions. Our results show that only one LSGM/LDC combination results in no additional phases. For the other combinations, at least one and often two additional phases, LaSrGaO₄ and LaSrGa₃O₇, result. Because LaSrGa₃O₇ has much lower conductivity, it is necessary to select combinations that avoid this phase. We propose that the combination that results in no additional phase should be considered favorably for SOFCs. For other LSGM compositions, LDC50 should be used as a buffer layer instead of LDC40 as is presently done in SOFC studies. Alternately, if LDC40 is preferred for buffer layer, then lower Sr content LSGM compositions should be used as electrolytes. These combinations are likely to lead to better long-term SOFC performance.     

A new structure of three-phase five-level inverter with nested two-level cells

This paper presents a new structure of three-phase five-level inverter with a single direct current (DC) source for low- and medium-voltage applications. The proposed configuration is built with a cascade connection of two-level cells in a nested form and owns the advantages of a reduced number of passive components, total blocking voltage of the switches, and isolated DC sources. In order to make this topology attractive, a comparison is made with five-level inverter topologies proposed for low- and medium-voltage applications in recent years. The proposed circuit is powered using a single DC source and an auxiliary voltage-balancing circuit (AVBC) to maintain the desired DC-link capacitor voltages. A sinusoidal pulse width modulation (SPWM) scheme is implemented in field-programmable gate array (FPGA), using Xilinx blocks developed in MATLAB/SIMULINK environment, to control the inverter switches. The performance of the proposed topology is verified through MATLAB simulation and prototype model for a step change in load. Finally, the experimental results are presented to validate the effectiveness of the proposed topology.     

Insight into cations substitution on structural and electrochemical properties of nanostructured Li2FeSiO4/C cathodes

Structural instability is the major obstacle in the Li₂FeSiO₄/C cathode during charge and discharge process, which can be improved by the substitution of cations in the host cage. In this study, the transition metal ions with different valence (Ag¹⁺, Zn²⁺, Cr³⁺, and Ti⁴⁺) have been substituted in Li₂FeSiO₄/C via modified sol-gel method and the impact on the structural, electrical, and electrochemical performances has been systematically explored. The Rietveld-refined XRD pattern and HR-TEM (SAED) result reveal that all the prepared samples maintain orthorhombic structure (S.G- Pmn2₁). The FE-SEM and TEM micrographs of bare and doped Li₂FeSiO₄/C display nanoparticle formation with 20-40 nm size. Among different cation-substituted silicates, Li₂Fe_0.9Ti_0.1SiO₄/C sample exhibits an excellent total conductivity of 1.20 × 10⁻⁴ S cm⁻¹ which is one order of magnitude higher than the bare Li₂FeSiO₄/C sample. The galvanostatic charge-discharge curves and cyclic voltammetric analysis reveal that the Li₂Fe_0.9Ti_0.1SiO₄/C material provides an excellent initial specific capacity of 242 mAh g⁻¹ and maintains a capacity of 226 mAh g⁻¹ after 50 cycles with capacity retention of 93.38%. The Ti doping is a promising strategy to overcome the capacity fading issues, by preventing the structural collapse during Li-ion intercalation/de-intercalation processes in the Li₂FeSiO₄/C electrode through the strong hybridization between the 3d and 4s orbitals in titanium and 2p orbital in oxygen.