Studies on the thermal properties of silicone polymer based thermal protection systems for space applications

Journal of Thermal Analysis and Calorimetry - Thermal decomposition, thermal conductivity, specific heat and flammability of polydimethyl siloxane (PDMS) resin and three PDMS-based systems with...     

Nanostructuring of 1-butyl-4-methylpyridinium chloride in ionic liquid–iron oxide nanofluids

Journal of Thermal Analysis and Calorimetry - Understanding the behavior of ionic liquids (ILs) in ionic liquid-based nanofluids has great significance for its proper application. The phase changes...     

Controlling decoherence via PT-symmetric non-Hermitian open quantum systems

We have studied the effect of a non-Hermitian Bosonic bath on the dynamics of a two-level spin system. The non-Hermitian Hamiltonian of the bath is chosen such that it converges to the harmonic oscillator Hamiltonian when the non-Hermiticity is switched off. We calculate the dynamics of the spin system and found that the non-Hermiticity can have positive as well as negative effects on the coherence of the system. However, the decoherence can be completely eliminated by choosing the non-Hermiticity parameter and the phase of the system bath interaction appropriately. We have also studied the effect of this bath on the entanglement of a two-spin system when the bath is acting only on one spin.     

Passive Boundary Layer Flow Control Using Porous Lamination

The flow over a porous laminated flat plate is investigated from a flow control perspective through experiments and computations. A square array of circular cylinders is used to model the porous lamination. We determine the velocities at the fluid–porous interface by solving the two-dimensional Navier–Stokes and the continuity equations using a staggered flow solver and using LDV in experiments. The control parameters for the porous region are porosity, \(\phi \) and Reynolds number, Re, based on the diameter of the circular cylinders used to model the porous lamination. Computations are conducted for \(0.4< \phi < 0.9\) and \(25< Re < 1000\), and the experiments are conducted for \(\phi = 0.65\) and 0.8 at \(Re \approx 391,\ 497\) and 803. The permeability of the porous lamination is observed to induce a slip velocity at the interface, effectively making it a slip wall. The slip velocity is seen to be increasing functions of \(\phi \) and Re. For higher porosities at higher Re, the slip velocity shows non-uniform and unsteady behavior and a breakdown Reynolds number is defined based on this characteristic. A map demarcating the two regimes of flow is drawn from the computational and experimental data. We observe that the boundary layer over the porous lamination is thinner than the Blasius boundary layer and the shear stress is higher at locations over the porous lamination. We note that the porous lamination helps maintain a favorable pressure gradient at the interface which delays separation. The suitable range of porosities for effective passive separation control is deduced from the results.     

Photoluminescence study on amino functionalized dysprosium oxide–zinc oxide composite bifunctional nanoparticles

An organic dispersion of 9–15 nm size stable dysprosium oxide incorporated zinc oxide nanocomposites exhibiting luminescence in the visible region has been synthesised by a wet chemical precipitation technique at room temperature. Tetraethoxysilane TEOS [(C₂H₅O)₄Si], (3-aminopropyl) trimethoxysilane (APTS) and a 1:1 mixture of TEOS–APTS have been used as capping agents to control the particle size as well as to achieve uniform dispersion of composite nanoparticles in methanol medium. X-ray diffractometer (XRD) analysis reveals the formation phase of amino-functionalised colloidal dysprosium oxide incorporated ZnO composite nanoparticles to be of zincite structure. The Transmission Electron Microscopy (TEM) images show that the particles are spheroids in shape, having average crystalline sizes ranging from 9 to 15 nm. The photoluminescence (PL) observed in these composites has been attributed to the presence of near band edge excitonic emission and existence of defect centres. The time correlated single photon counting studies of the composite nanoparticles exhibited three decay pathways. The enhanced PL emission intensity of solid state fluorescence spectra of samples is attributed to the absence of vibrational relaxation process.     

An expedient synthesis of spirooxindoles incorporating 2-amino pyran-3-carbonitrile unit employing dialkyl acetone-1,3-dicarboxylates

Spirooxindoles are a class of molecules possessing significant biological effects such as antiviral, antifungal, antibacterial and anticancer properties. Herein we report a series of spirooxindole molecules having 2-amino pyran-3-carbonitrile and with two ester groups. These molecules were prepared by the reaction of dialkyl acetone-1,3-dicarboxylate and isatilidenes in the presence of triethyl amine.     

Evaluation of the Probiotic Characteristics of Newly Isolated Lactic Acid Bacteria

Lactic acid bacteria were isolated from fermented vegetables, sour dough, milk products, sheep and human excreta. The newly isolated cultures were evaluated for a number of probiotic characteristics like bile salt resistance, salt tolerance in general, survival in low pH, hydrophobicity of the cell surface, resistance to low phenol concentration, antimicrobial activity and susceptibility pattern against vancomycin and erythromycin. The selected cultures were further screened for their ability to produce the nutraceticals such as folic acid and exopolysaccharide (EPS). Two potent isolates, CB2 (from cabbage) and SD2 (from sour dough) were found to produce both extracellular and intracellular folate. One of the isolates from yogurt (MC-1) and the one from whey (W3) produced significant amount of EPS with a maximum production of 8.79 +/- 0.05 g/l by MC-1.     

Selective colorimetric sensing of cysteine in aqueous solutions using silver nanoparticles in the presence of Cr³+

We here in report an extensive study on the development of a highly facile, selective and sensitive colorimetric probe for cysteine detection using silver nanoparticles (Ag NPs). The efficacy of the process relies upon the surface plasmon resonance properties of Ag NPs and the interaction of Ag-cysteine complex with chromium ions (Cr³⁺) in a ratio of 2:1. In the presence of Cr³⁺, cysteine was able to induce the aggregation of Ag NPs thereby resulting in a change in yellow colour of the Ag colloid to purple. The reported probe has a limit of detection down to 1 nM which is to the best of our knowledge the lowest ever reported for the colorimetric detection of cysteine. Furthermore, a remarkable feature of this method is that it involves a simple technique exhibiting high selectivity to cysteine over other tested amino acids.     

Laser-Assisted Scalable Pore Fabrication in Graphene Membranes for Blue-Energy Generation

The osmotic energy from a salinity gradient (i. e. blue energy) is identified as a promising non-intermittent renewable energy source for a sustainable technology. However, this membrane-based technology is facing major limitations for large-scale viability, primarily due to the poor membrane performance. An atomically thin 2D nanoporous material with high surface charge density resolves the bottleneck and leads to a new class of membrane material the salinity gradient energy. Although 2D nanoporous membranes show extremely high performance in terms of energy generation through the single pore, the fabrication and technical challenges such as ion concentration polarization make the nanoporous membrane a non-viable solution. On the other hand, the mesoporous and micro porous structures in the 2D membrane result in improved energy generation with very low fabrication complexity. In the present work, we report femtosecond (fs) laser-assisted scalable fabrication of μm to mm size pores on Graphene membrane for blue energy generation for the first time. A remarkable osmotic power in the order of μW has been achieved using mm size pores, which is about six orders of magnitudes higher compared to nanoporous membranes, which is mainly due to the diffusion-osmosis driven large ionic flux. Our work paves the way towards fs laser-assisted scalable pore creation in the 2D membrane for large-scale osmotic power generation.     

Folic Acid as a Bimodal Optical Probe for the Detection of TNT

Rapid and onsite detection of nitroaromatic explosive 2,4,6-trinitrotoluene (TNT) is very crucial for the safety and security of human life as well as for the environment. In this present work, we demonstrate the feasibility for employing Folic Acid (FA) as a fluorescent as well as a colorimetric probe for the detection of TNT. This probe was synthesized by a simple one-step process. The developed probe shows an emission maximum at 490 nm upon excitation at 420 nm. On adding TNT, the fluorescence of the FA probe is quenched. Also, it shows a good selectivity towards TNT over other similar organic compounds such as 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP) and picric acid (PA). The limit of detection (LoD) of TNT was found to be 1.9398 µM. Colorimetric detection was conducted and paper strip assay was developed for the practical applications.

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