Longitudinal Strain Dependent Variation of Poisson’s Ratio for HTPB Based Solid Rocket Propellants in Uni‐axial Tensile Testing

Poisson’s ratio of HTPB based composite propellant is estimated at break using double dumbbell specimens as per ASTM D638 Type IV standard and its value obtained by change in the volume of specimens is calculated as approximately 0.25. This major finding contradicts the behaviour of solid rocket propellants in respect of Poisson’s ratio, which is reported to be 0.5. Further, Poisson’s ratio varies almost linearly with strain even in linear portion of stress‐strain curve in uni‐axial tensile testing as per theoretical calculations. It must be noted that no change in volume does not necessarily indicate constant Poisson’s ratio equal to 0.5. SEM scan indicates that the rate of reduction of Poisson’s ratio with longitudinal strain accelerates after dewetting due to the formation of vacuoles. Bilinear variation of Poisson’s ratio with longitudinal strain is observed. One slope is valid in pre‐dewetting region, calculated from close form solution and other slope is valid for post‐dewetting region, which is measured at break. Measurement of Poisson’s ratio at various longitudinal strains indicates uni‐linear variation and not a bilinear variation with a kink. It is also observed that Poisson’s ratio is different along different lateral directions of the propellant specimen. Poisson’s ratio in two orthogonal directions perpendicular to longitudinal axis is calculated as 0.17 and 0.30. As ASTM Specimen has rectangular cross‐section of approximate size 6×4 mm, the directional behavior of Poisson’s ratio may be attributed to initial dimensions. Prismatic propellant specimen with square cross‐section of 115×6×6 mm dimension do not show any variation in respect of Young’s modulus, tensile strength and percentage elongation as compared to ASTM specimen. Directional behavior of Poisson’s ratio with almost similar numerical value is again observed, thus ruling out dependence of this behavior on different initial dimensions of propellant cross‐section. The propellant slurry flow during vacuum casting, directional curing and orientation of specimen with respect to web of the cast propellant are mainly responsible for this directional behaviour of Poisson’s ratio for the composite propellants. Composite propellants behave as compressible material in most of the region and near failure region or at higher strains; Poisson’s ratio is not anywhere close to 0.5, instead it is close to 0.25.     

Global estimates of evapotranspiration and gross primary production based on MODIS and global meteorology data

The simulation of gross primary production (GPP) at various spatial and temporal scales remains a major challenge for quantifying the global carbon cycle. We developed a light use efficiency model, called EC-LUE, driven by only four variables: normalized difference vegetation index (NDVI), photosynthetically active radiation (PAR), air temperature, and the Bowen ratio of sensible to latent heat flux. The EC-LUE model may have the most potential to adequately address the spatial and temporal dynamics of GPP because its parameters (i.e., the potential light use efficiency and optimal plant growth temperature) are invariant across the various land cover types. However, the application of the previous EC-LUE model was hampered by poor prediction of Bowen ratio at the large spatial scale. In this study, we substituted the Bowen ratio with the ratio of evapotranspiration (ET) to net radiation, and revised the RS-PM (Remote Sensing-Penman Monteith) model for quantifying ET. Fifty-four eddy covariance towers, including various ecosystem types, were selected to calibrate and validate the revised RS-PM and EC-LUE models. The revised RS-PM model explained 82% and 68% of the observed variations of ET for all the calibration and validation sites, respectively. Using estimated ET as input, the EC-LUE model performed well in calibration and validation sites, explaining 75% and 61% of the observed GPP variation for calibration and validation sites respectively.Global patterns of ET and GPP at a spatial resolution of 0.5° latitude by 0.6° longitude during the years 2000-2003 were determined using the global MERRA dataset (Modern Era Retrospective-Analysis for Research and Applications) and MODIS (Moderate Resolution Imaging Spectroradiometer). The global estimates of ET and GPP agreed well with the other global models from the literature, with the highest ET and GPP over tropical forests and the lowest values in dry and high latitude areas. However, comparisons with observed GPP at eddy flux towers showed significant underestimation of ET and GPP due to lower net radiation of MERRA dataset. Applying a procedure to correct the systematic errors of global meteorological data would improve global estimates of GPP and ET. The revised RS-PM and EC-LUE models will provide the alternative approaches making it possible to map ET and GPP over large areas because (1) the model parameters are invariant across various land cover types and (2) all driving forces of the models may be derived from remote sensing data or existing climate observation networks.     

Topological Quantum Phase Transition and Superconductivity Induced by Pressure in the Bismuth Tellurohalide BiTeI

A pressure‐induced topological quantum phase transition has been theoretically predicted for the semiconductor bismuth tellurohalide BiTeI with giant Rashba spin splitting. In this work, evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure‐dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted topological quantum phase transition in BiTeI. Superconductivity is observed in both BiTeI and BiTeBr, while resistivity at higher temperatures still exhibits semiconducting behavior. Theoretical calculations suggest that superconductivity may develop from the multivalley semiconductor phase. The superconducting transition temperature, T_c, increases with applied pressure and reaches a maximum value of 5.2 K at 23.5 GPa for BiTeI (4.8 K at 31.7 GPa for BiTeBr), followed by a slow decrease. The results demonstrate that BiTeX (X = I, Br) compounds with nontrivial topology of electronic states display new ground states upon compression.     

MgNb2O6:Dy3+ nanophosphor: A facile preparation,down conversion photoluminescence and UV driven photocatalytic properties

Series of (1–9 mol %) dysprosium (Dy³⁺) ions doped MgNb₂O₆ (MNO) nanophosphors were synthesized by chemical combustion process and their photo luminescent and photocatalytic behaviours were examined. Powder X-ray diffraction (PXRD) reveals the columbite structure and crystal structure parameters were calculated. The average crystallite size was found to be in the range of 20–30 nm as calculated by Scherrer's method. The photoluminescence (PL) of MgNb₂O₆:Dy³⁺ (λ_exc-393 nm) reflects white emission for the prepared samples as confirmed by CIE and CCT. The photocatalytic activities of these nanophosphors were probed for the decolorization of acid red 88 (AR-88) under UV light irradiation. The photocatalyst with MgNb₂O₆:Dy³⁺ (5 mol %) showed enhanced activity of 97%, attributed to effective separation of charge carriers. All the above experimental results confirm that, the optimized phosphor is quite useful for WLEDs, solid-state lighting applications and as a photocatalyst.     

Enhancement of Tensile and Microhardness of AA 6082-T6 Friction Stir Welds via Brass Interlayers

Russian Journal of Non-Ferrous Metals - This paper investigates the effects of brass interlayer on the microstructural and mechanical properties of friction stir welded AA 6082-T6. To analyze the...     

Synthesis and Humidity Sensing Properties of NiO Intercalated Polyaniline Nanocomposite

The exercising cooperative and interfacial properties of metal oxide and conducting polymer as a sensing material for humidity detection was the focal point of this study. In this piece of work nano sized NiO and its composite with polyaniline has been prepared. The cooperative effects of NiO on stuructural, morphology, humidity sensing behaviour of PANI has been investigated. Prepared materials were characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM),UV–VIS spectroscopy and Four probe techniques. The result reveals that the NiO strongly influences on polymer chain, crystallinity, stability, electrical and optical properties of PANI, which improves its viability in technology development. Finally, PANI/NiO was used for electrochemical humidity sensing of a closed atmosphere. The result reveals that 100 times increase in sensitivity of PANI due to the presence of NiO nano particles. Finally, the results indicate that the impact of NiO on PANI makes it promising perspective materials for humidity monitoring of closed chamber with improved sensing parameters over several method and materials.     

Numerical studies on evaluation of smoke control system of underground metro rail transport system in India having jet injection system: A case study

The rail based urban transport system is being developed for national capital of India, New Delhi. The smoke control using ventilation in case of fire inside the tunnel, similar to Delhi Metro corridor has been investigated using computational fluid dynamics technique. A section of tunnel having dimensions 400 m long, 5.5 m wide and 6 m high is considered for simulation. The analysis has been carried out by assuming a variable fire source with a peak heat release rate (HRR) of 16 MW, located at the center of the tunnel. Ventilation ducts are located in the ceiling near the tunnel portals and are inclined at 10 degrees to the plane of the ceiling through which fans discharge air. The influence of the fire HRR curve slope on the smoke flow dynamics in a realistic tunnel model fitted with jet injection type longitudinal ventilation system has been investigated. In case of fire two cases are studied: (1) fans activated immediately after detection, (2) fans activated at delayed times to take into account the response time for the fans to achieve its maximum speed. The velocity of supply and exhaust fans necessary to remove smoke in 30 s from the upstream direction is determined. The velocities of fan required to produce desired critical velocity in the longitudinal direction for different HRR of fire is predicted.     

Causes of seepage water in drainage and grouting galleries of the Pandoh Dam, Central Himalaya

At the Pandoh Dam in the Central Himalaya, a reddish brown material was observed seeping through drainage holes in three of the galleries. Initially considered to be phyllitic oxide, this was chemically analysed and found to be sulphate radicals. A sulphate concentration of 861.50 ppm was recorded in the seepage water. Petrography of the bedrocks and X-ray analysis of the suspended reddish brown powder as well as chemical analysis of the seepage water revealed the presence of chalcopyrite, pyrrhotite and the conversion of monosulphate phases into ettringite phases as the major cause of expansion and seepage. This process is accompanied by a significant volume increase which it was concluded was responsible for the internal stresses causing the cracking through which the seepage water entered the drainage and grouting galleries.     

Failure Analysis of AISI 440C Steel Ball Screws Used in the Actuator System of a Satellite Launch Vehicle

In view of its excellent wear and corrosion resistance, AISI 440C steel is the material of choice for the fabrication of ball screws used in actuator systems of satellite launch vehicles. During the routine acceptance test of a ball screw, longitudinal cracks were observed at the shaft location of the ball screw. The optical microstructure of the ball screw material (AISI 440C) revealed the presence of aligned carbides (carbide banding). Fractographic observations revealed the cracking to be along the carbide bands. Based on detailed optical and scanning electron microscopic observations, the cracking of the ball screws was attributed to the carbide bands.