Showing papers by "Vikram Sarabhai Space Centre published in 2016"

Aerosol and monsoon climate interactions over Asia

Abstract: The increasing severity of droughts/floods and worsening air quality from increasing aerosols in Asia monsoon regions are the two gravest threats facing over 60% of the world population living in Asian monsoon regions. These dual threats have fueled a large body of research in the last decade on the roles of aerosols in impacting Asian monsoon weather and climate. This paper provides a comprehensive review of studies on Asian aerosols, monsoons, and their interactions. The Asian monsoon region is a primary source of emissions of diverse species of aerosols from both anthropogenic and natural origins. The distributions of aerosol loading are strongly influenced by distinct weather and climatic regimes, which are, in turn, modulated by aerosol effects. On a continental scale, aerosols reduce surface insolation and weaken the land-ocean thermal contrast, thus inhibiting the development of monsoons. Locally, aerosol radiative effects alter the thermodynamic stability and convective potential of the lower atmosphere leading to reduced temperatures, increased atmospheric stability, and weakened wind and atmospheric circulations. The atmospheric thermodynamic state, which determines the formation of clouds, convection, and precipitation, may also be altered by aerosols serving as cloud condensation nuclei or ice nuclei. Absorbing aerosols such as black carbon and desert dust in Asian monsoon regions may also induce dynamical feedback processes, leading to a strengthening of the early monsoon and affecting the subsequent evolution of the monsoon. Many mechanisms have been put forth regarding how aerosols modulate the amplitude, frequency, intensity, and phase of different monsoon climate variables. A wide range of theoretical, observational, and modeling findings on the Asian monsoon, aerosols, and their interactions are synthesized. A new paradigm is proposed on investigating aerosol-monsoon interactions, in which natural aerosols such as desert dust, black carbon from biomass burning, and biogenic aerosols from vegetation are considered integral components of an intrinsic aerosol-monsoon climate system, subject to external forcing of global warming, anthropogenic aerosols, and land use and change. Future research on aerosol-monsoon interactions calls for an integrated approach and international collaborations based on long-term sustained observations, process measurements, and improved models, as well as using observations to constrain model simulations and projections.

Strain hardening of Titanium alloy Ti6Al4V sheets with prior heat treatment and cold working

Abstract: Strain hardening of Titanium alloy Ti6Al4V has been studied at four different strain rates (10 −4 to 10 −1 s −1 ) under tensile loading at four different heat treatment conditions viz. mill annealing (MA), recrystallization annealing (RA), solution treatment (ST) and solution treatment and aging (STA). Effect of prior cold working before tensile testing has also been studied. Strain hardening exponent (n) is found to be decreasing with increasing strain rates for samples in all the four heat treatment conditions, whereas trend is found to be opposite in case, of cold worked (~15%) samples prior to tensile testing. This is due to rearrangement of dislocations generated during the prior cold working. Strength coefficient (K) is also found to follow similar trend. Optical microstructure clearly showed two phase (α+β) structure in all the samples and completely fragmented grain boundaries in cold worked condition. Non-basal oriented grains in as-annealed samples and higher volume fraction of basal (0001) grains in annealed and cold worked samples were observed along with fragmented grain boundaries/regions of void coalescence. Low angle misorientation was found to be lower in sample subjected to STA heat treatment as compared to other heat treated conditions. Twinning was observed in ST as well as in STA conditions, which was absent in annealed as well as annealed and cold worked samples. Image quality maps revealed regions of low image quality in deformed samples indicating presence of high dislocation density. Regions of void coalescence were confirmed by KAM (Kernel average misorientation) maps, GOS (grain orientation spread) maps and unique grain colour maps. Analysis of fractographs showed ductile mode of fracture in all heat treated conditions and mixed mode of fracture with fragmented grain boundaries in all samples subjected to heat treatment followed by tensile testing with prior cold working.

A robust, melting class bulk superhydrophobic material with heat-healing and self-cleaning properties.

Abstract: Superhydrophobic (SH) materials are essential for a myriad of applications such as anti-icing and self-cleaning due to their extreme water repellency. A single, robust material simultaneously possessing melt-coatability, bulk water repellency, self-cleanability, self-healability, self-refreshability, and adhesiveness has been remaining an elusive goal. We demonstrate a unique class of melt-processable, bulk SH coating by grafting long alkyl chains on silica nanoparticle surface by a facile one-step method. The well-defined nanomaterial shows SH property in the bulk and is found to heal macro-cracks on gentle heating. It retains wettability characteristics even after abrading with a sand paper. The surface regenerates SH features (due to reversible self-assembly of nano structures) quickly at ambient temperature even after cyclic water impalement, boiling water treatment and multiple finger rubbing tests. It exhibits self-cleaning properties on both fresh and cut surfaces. This kind of coating, hitherto undisclosed, is expected to be a breakthrough in the field of melt-processable SH coatings.

High Performing Biobased Ionic Liquid Crystal Electrolytes for Supercapacitors

Abstract: Production and storage of energy in a highly efficient and environmentally sustainable way is a demand of the current century to meet the growing global energy requirement. Design and development of novel materials and processes that allow precise control over the electrochemical behavior and conductivity of electrolytes is necessary for acquiring such targets. Development of ionic liquid crystals with ordered domains endowed with enhanced ionic conductivity from renewable resources is receiving much interest in this respect. In this paper, we report a unique strategy for the preparation and utilization of ionic liquid crystalline electrolyte derived from a renewable resource: cashew nut shell liquid; an abundantly available waste byproduct from cashew industry. We have prepared imidazolium-based ionic liquid crystal (PMIMP) from cardanol and studied its structure and liquid crystalline phase formation by various techniques. The symmetrical supercapacitor fabricated with mesoporous carbon electrodes emplo...

Graphite oxide–iron oxide nanocomposites as a new class of catalyst for the thermal decomposition of ammonium perchlorate

Abstract: Graphite oxide (GO) is receiving increased attention due to its special surface properties and layered structure for the synthesis of GO containing nanocomposites. It is possible that integration of GO sheets and iron oxide nanoparticles may result in enhanced properties and enlarge the application range. Herein, we report the effect of Fe2O3–GO nanocomposite as a new class of catalyst for the decomposition of ammonium perchlorate (AP), a rocket propellant oxidizer, and study the effect of Fe2O3 : GO ratio on the catalytic activity. The material was characterized by X-ray diffraction and Raman spectroscopy and the formation of Fe2O3 and GO were confirmed. FESEM analysis showed that the Fe2O3 nanoparticles are highly dispersed between and on the graphene layers. With the addition of 3% of the composite with 1 : 1 Fe2O3–GO ratio, the decomposition temperature of AP was reduced by 45 °C, showing a high catalytic activity for the new composite. The high catalytic activity of the in situ synthesized Fe2O3–GO composite may be attributed to the uniform distribution of iron oxide nanoparticles which in turn provide a number of active sites on the surface due to the presence of GO.

Diurnal variability of the atmospheric boundary layer height over a tropical station in the Indian monsoon region

Abstract: . The diurnal variation of atmospheric boundary layer (ABL) height is studied using high-resolution radiosonde observations available at 3 h intervals for 3 days continuously from 34 intensive campaigns conducted during the period December 2010–March 2014 over a tropical station Gadanki (13.5° N, 79.2° E; 375 m), in the Indian monsoon region. The heights of the ABL during the different stages of its diurnal evolution, namely, the convective boundary layer (CBL), the stable boundary layer (SBL), and the residual layer (RL) are obtained to study the diurnal variabilities. A clear diurnal variation is observed in 9 campaigns out of the 34 campaigns. In 7 campaigns the SBL did not form in the entire day and in the remaining 18 campaigns the SBL formed intermittently. The SBL forms for 33–55 % of the time during nighttime and 9 and 25 % during the evening and morning hours, respectively. The mean SBL height is within 0.3 km above the surface which increases slightly just after midnight (02:00 IST) and remains almost constant until the morning. The mean CBL height is within 3.0 km above the surface, which generally increases from morning to evening. The mean RL height is within 2 km above the surface which generally decreases slowly as the night progresses. The diurnal variation of the ABL height over the Indian region is stronger during the pre-monsoon and weaker during winter season. The CBL is higher during the summer monsoon and lower during the winter season while the RL is higher during the winter season and lower during the summer season. During all the seasons, the ABL height peaks during the afternoon (∼ 14:00 IST) and remains elevated until evening (∼ 17:00 IST). The ABL suddenly collapses at 20:00 IST and increases slightly in the night. Interestingly, it is found that the low level clouds have an effect on the ABL height variability, but the deep convective clouds do not. The lifting condensation level (LCL) is generally found to occur below the ABL for the majority of the database and they are randomly related.

Corrosion and nanomechanical behaviors of plasma electrolytic oxidation coated AA7020-T6 aluminum alloy

Abstract: Alumina coating was deposited on AA7020 aluminum alloy by plasma electrolytic oxidation (PEO) method. The corrosion, stress corrosion cracking (SCC) and nano-mechanical behaviors were examined by means of potentiodynamic polarization, slow strain rate test (SSRT) and nano-indentation tests. Potentiodynamic polarization (PP) was used to evaluate the corrosion resistance of the coating and slow strain rate test (SSRT) was used for evaluating the environmental cracking resistance in 3.5% NaCl solution. The mechanical properties (hardness and elastic modulus) were obtained from each indentation as a function of the penetration depth across the coating cross section. The above results were compared with similar PEO coated aluminum and magnesium alloys. Results indicated that PEO coating on AA7020 alloy significantly improved the corrosion resistance. However the environmental cracking resistance was found to be only marginal. The hardness and elastic modulus values were found to be much higher when compared to the base metal and similar PEO coated 7075 aluminum alloys. The fabricated coating also exhibited good adhesive strength with the substrate similar to other PEO coated aluminum alloys reported in the literature

Effect of tropical cyclones on the stratosphere–troposphere exchangeobserved using satellite observations over the north Indian Ocean

Abstract: . Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere–troposphere exchange (STE) processes in the upper troposphere and lower stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the north Indian Ocean during 2007–2013 on the STE processes is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) radio occultation (RO) measurements, and ozone and water vapour concentrations in the UTLS region are obtained from Aura Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km of the centre of the tropical cyclone. In our earlier study, we observed a decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K), and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within 500 km of the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from the cyclone centre, whereas the enhancement in the water vapour in the lower stratosphere is more significant on the south-east side, extending from 500 to 1000 km away from the cyclone centre. The cross-tropopause mass flux for different intensities of cyclones is estimated and it is found that the mean flux from the stratosphere to the troposphere for cyclonic storms is 0.05 ± 0.29 × 10−3 kg m−2, and for very severe cyclonic storms it is 0.5 ± 1.07 × 10−3 kg m−2. More downward flux is noticed on the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget, and consequentially the STE in the UTLS region.

Microstructure and micro-texture evolution during large strain deformation of aluminium alloy AA 2219

Abstract: Aluminium alloy AA2219 is widely used in the fabrication of propellant tanks of cryogenic stages of satellite launch vehicles. These propellant tanks are welded structures and a fine grained microstructure is usually preferred for sheets/plates and ring rolled rings used in their fabrication. In order to study the effect of large strain deformation on the microstructural evolution, hot isothermal plane strain compression (PSC) tests were conducted on AA 2219 in the temperature range of 250 °C–400 °C and at strain rates of 0.01 s −1 and 1 s −1 . Flow curves obtained at different temperatures and strain rates exhibited two types of behavior; one with a clear stress peak followed by softening, occurring below Z=2.5E+15 and steady state flow behavior above it. Electron Back-Scatter Diffraction (EBSD) analysis of the PSC tested samples at the location of maximum strain revealed the presence of lamellar microstructures with very low fraction of transverse high angle boundaries (HABs). The loss of HABs during large strain deformation is attributed to the occurrence of dynamic recovery (DRV) as the ratio of calculated to measured lamellar boundary width is less than unity. Based on detailed microstructure and micro texture analysis, it was concluded that it is very difficult to obtain large fraction of HABs through uniaxial large strain deformation. Therefore, to obtain fine grain microstructure in thermo-mechanically processed AA2219 products, multi-axial deformation is essential.

Variations in O 3 , CO, and CH 4 over the Bay of Bengal during the summer monsoon season: shipborne measurements and model simulations

Abstract: . We present shipborne measurements of surface ozone (O3), carbon monoxide (CO), and methane (CH4) over the Bay of Bengal (BoB), the first time such measurements have been performed during the summer monsoon season, as a part of the Continental Tropical Convergence Zone (CTCZ) experiment during 2009. O3, CO, and CH4 mixing ratios exhibited significant spatial and temporal variability in the ranges of 8–54 nmol mol−1, 50–200 nmol mol−1, and 1.57–2.15 µmol mol−1, with means of 29.7 ± 6.8 nmol mol−1, 96 ± 25 nmol mol−1, and 1.83 ± 0.14 µmol mol−1, respectively. The average mixing ratios of trace gases over BoB in air masses from central/northern India (O3: 30 ± 7 nmol mol−1; CO: 95 ± 25 nmol mol−1; CH4: 1.86 ± 0.12 µmol mol−1) were not statistically different from those in air masses from southern India (O3: 27 ± 5 nmol mol−1; CO: 101 ± 27 nmol mol−1; CH4: 1.72 ± 0.14 µmol mol−1). Spatial variability is observed to be most significant for CH4 with higher mixing ratios in the air masses from central/northern India, where higher CH4 levels are seen in the SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY) data. O3 mixing ratios over the BoB showed large reductions (by ∼ 20 nmol mol−1) during four rainfall events. Temporal changes in the meteorological parameters, in conjunction with O3 vertical profile, indicate that these low-O3 events are associated with downdrafts of free-tropospheric O3-poor air masses. While the observed variations of O3 and CO are successfully reproduced using the Weather Research and Forecasting model with Chemistry (WRF-Chem), this model overestimates mean concentrations by about 6 and 16 % for O3 and CO, respectively, generally overestimating O3 mixing ratios during the rainfall events. An analysis of modelled O3 along air mass trajectories show mean en route O3 production rate of about 4.6 nmol mol−1 day−1 in the outflow towards the BoB. Analysis of the various tendencies from model simulations during an event on 10 August 2009, reproduced by the model, shows horizontal advection rapidly transporting O3-rich air masses from near the coast across the BoB. This study fills a gap in the availability of trace gas measurements over the BoB and, when combined with data from previous campaigns, reveals large seasonal amplitude ( ∼ 39 and ∼ 207 nmol mol−1 for O3 and CO, respectively) over the northern BoB.

Strengthening in high strength Cu-Cr-Zr-Ti alloy plates produced by hot rolling

Abstract: The aim of present investigation was to achieve different combination of strength and ductility in Cu-Cr-Zr-Ti alloy by multi-pass rolling in the temperature range of 500–800 °C. The hot rolled specimens were characterized for microstructure and mechanical properties by optical microscopy, transmission electron microscopy, and tensile testing. Specimens rolled in the aforementioned temperature range showed yield strength better than that of solution treated condition. Combination of high strength and good ductility was achieved by rolling at 500 °C with ultimate tensile strength, yield strength, and ductility of 349 MPa, 318 MPa, and 26% respectively. The superior strength achieved by rolling at 500 °C has been attributed to formation of fine chromium precipitates and high dislocation density.

Influence of tropical cyclones on tropospheric ozone: possible implications

Abstract: . The present study examines the role of tropical cyclones in the enhancement of tropospheric ozone. The most significant and new observation reported is the increase in the upper-tropospheric (10–16 km) ozone by 20–50 ppbv, which has extended down to the middle (6–10 km) and lower troposphere (

Organic and inorganic components of aerosols over the central Himalayas: winter and summer variations in stable carbon and nitrogen isotopic composition

Abstract: The aerosol samples were collected from a high elevation mountain site, Nainital, in India (1958 m asl) during September 2006 to June 2007 and were analyzed for water-soluble inorganic species, total carbon, nitrogen, and their isotopic composition (δ(13)C and δ(15)N, respectively). The chemical and isotopic composition of aerosols revealed significant anthropogenic influence over this remote free-troposphere site. The amount of total carbon and nitrogen and their isotopic composition suggest a considerable contribution of biomass burning to the aerosols during winter. On the other hand, fossil fuel combustion sources are found to be dominant during summer. The carbon aerosol in winter is characterized by greater isotope ratios (av. -24.0‰), mostly originated from biomass burning of C4 plants. On the contrary, the aerosols in summer showed smaller δ(13)C values (-26.0‰), indicating that they are originated from vascular plants (mostly of C3 plants). The secondary ions (i.e., SO4 (2-), NH4 (+), and NO3 (-)) were abundant due to the atmospheric reactions during long-range transport in both seasons. The water-soluble organic and inorganic compositions revealed that they are aged in winter but comparatively fresh in summer. This study validates that the pollutants generated from far distant sources could reach high altitudes over the Himalayan region under favorable meteorological conditions.

High strength toughened epoxy nanocomposite based on poly(ether sulfone)-grafted multi-walled carbon nanotube

Abstract: Hydroxyl terminated poly(ether sulfone) (PES) has been grafted on multi-walled carbon nanotube (MWCNT). The grafting reaction was confirmed by different characterization techniques such as Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and transmission electron microscopy. The extent of the grafting was found to be around 58 wt%. Hybrid nanocomposite of epoxy with the modified MWCNT was also prepared. Effect of grafting on the mechanical, thermal, and viscoelastic properties was studied. Dynamic mechanical studies show an increase in the storage modulus for the nanocomposite prepared using PES-grafted MWCNT compared with neat epoxy system. PES-grafted MWCNT–epoxy nanocomposite induces a significant increase in both tensile strength (26%) and fracture toughness (125%) of the epoxy matrix. Field emission scanning electron micrographs of fractured surfaces were examined to understand the toughening mechanism. Copyright © 2015 John Wiley & Sons, Ltd.

Deformation behavior of commercially pure (CP) titanium under equi-biaxial tension

Abstract: Biaxial tensile tests on commercially pure titanium were carried out using cruciform specimen geometry and the effect of biaxial tensile stress state on the mechanical properties was discussed. An optimum cruciform specimen geometry obtained using a commercial FE code was subjected to equi-biaxial tensile loading and the load-strain response was captured using data acquisition system. In addition, non-contact digital image correlation technique was employed for the measurement of failure strain. It is observed that the ultimate tensile strength approximately doubled and the failure strain decreased in contrast to uniaxial mechanical properties of commercially pure titanium. Increased effective modulus under biaxial condition is justified based on the generalized Hooke’s relation. Strong basal and split-basal texture components of as-received sample resulted in biaxial strengthening effect. Significant textural evolution observed upon biaxial deformation can be attributed to constrained deformation under such stress state.

Effect of Ni content on the diffusion-controlled growth of the product phases in the Cu(Ni)-Sn system

Abstract: A strong influence of Ni content on the diffusion-controlled growth of the (Cu,Ni)3Sn and (Cu,Ni)6Sn5 phases by coupling different Cu(Ni) alloys with Sn in the solid state is reported. The continuous increase in the thickness ratio of (Cu,Ni)6Sn5 to (Cu,Ni)3Sn with the Ni content is explained by combined kinetic and thermodynamic arguments as follows: (i) The integrated interdiffusion coefficient does not change for the (Cu,Ni)3Sn phase up to 2.5 at.% Ni and decreases drastically for 5 at.% Ni. On the other hand, there is a continuous increase in the integrated interdiffusion coefficient for (Cu,Ni)6Sn5 as a function of increasing Ni content. (ii) With the increase in Ni content, driving forces for the diffusion of components increase for both components in both phases but at different rates. However, the magnitude of these changes alone is not large enough to explain the high difference in the observed growth rate of the product phases because of Ni addition. (iv) Kirkendall marker experiments in...