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Influence of surface commensurability on the structure and relaxation dynamics of a confined monatomic fluid
No full textMolecular dynamics simulations are carried out for a single component, monatomic Lennard-Jones fluid confined between two mica surfaces to investigate the structure and relaxation dynamics of the confined fluid as a function of surface separation. Due to the underlying symmetry of the potassium ions on the mica surface, the contact layers prefer to adopt an incommensurate square or rhombic symmetry. The inner layers adopt a symmetry varying between rhombic, triangular, and square, depending on the density and surface separation. When the surface separation is an integral multiple of the particle diameter, distinct layering is observed, whereas jammed layers are formed at intermediate surface separations. This leads to the formation of both commensurate and incommensurate layering with varying intralayer symmetry. The self-intermediate scattering function exhibits a gamut of rich dynamics ranging from a distinct two-step relaxation indicative of glassy dynamics to slow relaxation processes where the correlations do not relax to zero over a microsecond for specific surface separations. An extended beta relaxation is observed for both commensurate and incommensurate layering. Stretched exponential fits are used to obtain the relaxation times for the late alpha-relaxation regime of the self-intermediate scattering function. In some cases, we also observed dynamic and structural heterogeneities within individual layers. Although a single-component Lennard-Jones fluid does not exhibit a glass transition in the bulk, this study reveals that such a fluid can display, without supercooling, complex relaxation dynamics with signatures of a fluid approaching a glass transition upon confinement at constant temperature. Published by AIP Publishing
Waste to Wealth Concept: Disposable RGO Filter Paper for Flexible Temperature Sensor Applications
No full textWe have developed a flexible reduced graphene oxide (RGO) temperature sensor on filter paper based cellulose substrate using vacuum filtration method. One of the most commonly used synthesized methods for RGO thin films is vacuum filtration process. It has several advantages such as simple operation and good controllability. The structural analysis was carried out by FE-SEM, in which the surface morphology images confirm the formation of RGO nanostructures on the filter paper substrate. It was observed that the pores of the filter paper were completely filled with the RGO material during the filtration process, subsequently the formation of continuous RGO thin films. As a results, the RGO films exhibits a piezoresistive property. The resulted RGO based films on the filter paper reveals the semiconducting behavior having sensitivity of 0.278 Omega/degrees C and negative temperature coefficient (NTC) about -0.00254 Omega / Omega /degrees C. Thus, we demonstrate a simplified way for the fabrication of RGO films on filter paper that possesses better and easier measurable macroscopic electrical properties. Our approach is for easy way of electronics, cost-effective and environment friendly fabrication route for flexible conducting graphene films on filter paper. This will enable for the potential applications in flexible electronics in various fields including biomedical, automobile and aerospace engineering
A critical assessment of tar generated during biomass gasification - Formation, evaluation, issues and mitigation strategies
No full textBiomass gasification receives attention as a promising method to utilize biomass, a fuel which is carbon neutral. The producer gas/syngas which is an energy carrier obtained through this method finds use in engines, fuel cells, Fischer-Tropsch reactors, methanol synthesis and as an input for chemical industries, after the required quality levels for the above applications are achieved. To use the producer gas/syngas for power generation on a commercial scale, the required gas quality has to be established. Producer gas obtained from biomass gasification has several contaminants like particulate matter, tar and gaseous species like H2S, NH3. The contaminants present in the producer gas, depending upon their nature and the amount, pose issues to power generation systems. Tar, which is a mixture of varying molecular weight hydrocarbon molecules, generated from the thermo-chemical conversion processes of organic materials, could condense at low temperatures, and lead to clogging or blockage in end-use application devices, filters, and fuel lines. So, it is essential to reduce or transform the tar present in the producer gas to utilize the biomass gasification systems for power generation. This paper attempts to provide a critical assessment of tar generated during biomass gasification, covering the sundry aspects of formation, evaluation, issues and mitigation strategies. The paper gives an introduction to biomass gasification systems, followed by a detailed description of tar, including the definition and the chemistry of formation and destruction. An explanation of the various aspects of tar sampling, characterization and analysis, is presented next. The suitability of different tar analysis approaches is compared from an end-use device perspective. Then the multifarious issues posed by the presence of tar in the syngas on the end-use devices is discussed. The last part of the paper describes several tar mitigation strategies used by researchers
Dwarf irregular galaxies with extended HI gas disks: Suppression of small-scale spiral structure by dark matter halo
No full textDwarf irregular galaxies with extended HI disk distributions, such as DDO 154, allow measurement of rotation curves, hence deduction of dark matter halo properties to large radial distances, up to several times the optical radius. These galaxies contain a huge reservoir of dark matter halo, which dominates over most of disk. We study the effect of the dark matter halo on small-scale spiral features by carrying out the local, non-axisymmetric perturbation analysis in the disks of five such late-type, gas-rich dwarf irregular galaxies, namely, DDO 154, NGC 3741, DDO 43, NGC 2366, and DDO 168 which host a dense and compact dark matter halo. We show that when the gas disk is treated alone, it allows a finite swing amplification; which would result in small-scale spiral structure in the outer gas disk, but the addition of dark matter halo in the analysis results in a higher Toomre Q parameter which prevents the amplification almost completely. This trend is also seen to be true in regions inside the optical radius. This implies absence of strong small-scale spiral arms in these galaxies, which is in agreement with observations. Hence despite being gas-rich, and in fact having gas as the main baryonic component, these galaxies cannot support small-scale spiral structure which would otherwise have been expected in normal gas rich galaxies
Challenges in application of Raman spectroscopy to biology and materials
No full textRaman spectroscopy has become an essential tool for chemists, physicists, biologists and materials scientists. In this article, we present the challenges in unravelling the molecule-specific Raman spectral signatures of different biomolecules like proteins, nucleic acids, lipids and carbohydrates based on the review of our work and the current trends in these areas. We also show how Raman spectroscopy can be used to probe the secondary and tertiary structural changes occurring during thermal denaturation of protein and lysozyme as well as more complex biological systems like bacteria. Complex biological systems like tissues, cells, blood serum etc. are also made up of such biomolecules. Using mice liver and blood serum, it is shown that different tissues yield their unique signature Raman spectra, owing to a difference in the relative composition of the biomolecules. Additionally, recent progress in Raman spectroscopy for diagnosing a multitude of diseases ranging from cancer to infection is also presented. The second part of this article focuses on applications of Raman spectroscopy to materials. As a first example, Raman spectroscopy of a melt cast explosives formulation was carried out to monitor the changes in the peaks which indicates the potential of this technique for remote process monitoring. The second example presents various modern methods of Raman spectroscopy such as spatially offset Raman spectroscopy (SORS), reflection, transmission and universal multiple angle Raman spectroscopy (UMARS) to study layered materials. Studies on chemicals/layered materials hidden in non-metallic containers using the above variants are presented. Using suitable examples, it is shown how a specific excitation or collection geometry can yield different information about the location of materials. Additionally, it is shown that UMARS imaging can also be used as an effective tool to obtain layer specific information of materials located at depths beyond a few centimeters
Raceway Formation in a Moving Bed
No full textRaceway is formed in the blast furnace when high velocity air is blown into a bed of coke particles. The blast furnace is treated as a moving bed as the burden descends to replace the coke particles consumed by the combustion in front of the tuyeres. In this study, an experimental setup is constructed using Perspex sheet to replicate the moving bed and a detailed study of raceway size is carried out with respect to different parameters such as gas velocity, bed height and particles flow rate. Compressed air is used as the gas phase and granules of Linear Low Density Polyethylene (LLDPE) are used as the packing particles. Results confirm the existence of the cavity hysteresis phenomenon in a stationary packed bed. For moving beds, it is found that the cavity hysteresis phenomenon is absent, except at a very low particles flow rate. It is also observed that raceway size in the moving bed is independent of the bed height and solid mass flow rate, except for a very low solid/particles flow rates. Results confirm the previous hypothesis that if there are no frictional forces then there would not be any raceway hysteresis in the system. The study also confirms that the raceway size obtained in a stationary packed bed for decreasing gas velocity condition is similar to that obtained in the moving beds
The Role of Reactive Oxygen Species and Ferroptosis in Heme-Mediated Activation of Human Platelets
No full textHemolysis, a process by which the destruction of red blood cells leads to the release of hemoglobin, is a critical event observed during hemolytic disorders. Under oxidative stress conditions, hemoglobin can release its heme prosthetic group, which is highly cytotoxic and can catalyze the generation of reactive oxygen species (ROS), leading to several undesired redox reactions in the cells. Herein, we demonstrate for the first time that heme can mediate the activation and death of human platelets through ferroptosis, which is an iron-dependent form of nonapoptotic cell death. This study also suggests that the heme-mediated lipid peroxidation and ferroptosis in platelets may play an important role in hemolytic disorders
Out-of-plane flexure behaviour of fly ash-lime-gypsum brick masonry walls
No full textIndustrial by-products such as fly ash is being used for the manufacture of building products such as fly ash bricks. This paper is focused on understanding the out of plane flexural behaviour of fly ash-lime-gypsum (FaL-G) brick masonry, through experimental investigations. Results of the flexure strength of FaL-G brick masonry walls (under different pre-compression) in the two orthogonal directions, are discussed. Load displacement and moment-curvature relationships for the two cases presented. The cracking flexural stress using linear elastic analysis was predicted and compared with the experimental value. The results reveal that (a) the flexure strength of FaL-G brick masonry walls increases linearly with the increase in pre-compression, (b) the flexure strength parallel to bed joints is two times more than that of the flexure strength perpendicular to bed joints under zero pre-compression, (c) lateral displacements for the FaL-G brick masonry walls are larger for the case of bending perpendicular to bed joints when compared with those for bending parallel to bed joints and (d) The cracking flexural stress for the FaL-G brick masonry can be predicted closely with those of experimental values using linear elastic analysis
Flux transport dynamo: From modelling irregularities to making predictions
No full textThe flux transport dynamo, in which the poloidal magnetic field is generated by the Babcock Leighton mechanism and the meridional circulation plays a crucial role, has emerged as an attractive model for the solar cycle. Based on theoretical calculations done with this model, we argue that the fluctuations in the Babcock Leighton mechanism and the fluctuations in the meridional circulation are the most likely causes of the irregularities of the solar cycle. With our increased theoretical understanding of how these irregularities arise, it can be possible to predict a future solar cycle by feeding the appropriate observational data in a theoretical dynamo model
Nonlinear optical properties of lead-free ferroelectric nanostructured perovskite
No full textLead-free perovskite materials with superior physical properties are currently explored for ferroelectric and optoelectronic applications. Ferroelectric materials that have large spontaneous polarization concomitantly possess large nonlinear optical response which is highly suitable for novel photonic applications. Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) is one such novel lead-free ferroelectric material with large piezoelectric response arising from existence of morphotropic phase boundary. Conventional sol-gel technique was adopted for synthesizing nanostructured BCZT (nano-BCZT) powder using citrate precursor route. X-ray powder diffraction confirmed the phase purity and high-resolution transmission electron microscopy (HRTEM) proved that the as-synthesized BCZT was indeed nanostructured. Supportively, Raman vibrational analysis was employed to validate the site occupancies of dopants and structural correlations when compared to undoped and pristine barium titanate. Nanostructured barium titanate is extensively studied as biomarkers in second harmonic generation (SHG) microscopy for bio-medical applications. In our current work, we have explored both second- and third-order nonlinear optical response of nano-BCZT. These were found to exhibit stronger SHG signal than potassium di-hydrogen phosphate (KDP) which is a well-known SHG standard. Subsequently, we also have investigated their third-order nonlinear optical properties using open aperture Z-scan technique at 532-nm excitation wavelength in the nanosecond regime. Nano-BCZT was found to exhibit strong two-photon absorption behavior. Such materials with multiphoton absorption behavior are favorable for nonlinear photonics devices such as optical limiters and contrast agents in nonlinear optical microscopy