Thermo-acoustics and its detection in a premixed flame

A new optical technique based on light-matter interaction is devised in-house to detect thermo-acoustic disturbances generated after ignition and during propagation of a premixed flame front in a half open channel. The technique involves passing a polarized laser light through a medium whose density or refractive index varies due to the passage of acoustic waves and/or flame front and then capturing the leaked depolarised light through an analyser by a photo-detector. The technique is applied to combustor involving premixed flame propagation and tulip inversion. The thermo-acoustic signals and the flame front are distinguished by comparing the oscilloscope signal with high speed photography of the flow-field. Acoustic waves are found to intercept the flame propagation at various axial locations and time instants

The conversion of Neutron star to Strange star : A two step process

The conversion of neutron matter to strange matter in a neutron star have been studied as a two step process. In the first step, the nuclear matter gets converted to two flavour quark matter. The conversion of two flavour to three flavour strange matter takes place in the second step. The first process is analysed with the help of equations of state and hydrodynamical equations, whereas, in the second process, non-leptonic weak interaction plays the main role. Velocities and the time of travel through the star of these two conversion fronts have been analysed and compared.Comment: 18 pages including 9 figure

Solar Magnetoseismology with Magnetoacoustic Surface Waves in Asymmetric Magnetic Slab Waveguides

Solar magnetoseismology is an indirect method to approximate plasma parameters that are traditionally difficult to measure in the solar atmosphere using observations of magnetohydrodynamic waves. A magnetic slab can act as waveguide for magnetoacoustic waves that approximates magnetic structures in the solar atmosphere. The asymmetry of the slab caused by different plasma parameters in each external region affects both the eigenfrequencies and eigenfunctions differently at each side of the slab, that is, both the temporal and spatial profiles of the eigenmodes of propagation along the slab are influenced by the equilibrium asymmetry. We present two novel diagnostic tools for solar magnetoseismology that use this distortion to estimate the slab magnetic field strength using the spatial distribution of magnetoacoustic surface waves: the amplitude ratio and the minimum perturbation shift techniques. They have the potential to estimate background equilibrium parameters in inhomogeneous solar structures such as elongated magnetic bright points, prominences, and the clusters of magnetic brightenings rooted in sunspot light bridges known as light bridge surges or light walls, which may be locally approximated as slabs

A review of the genome, epidemiology, clinical features, prevention, and treatment scenario of COVID-19: Bangladesh aspects

Abstract Background The ongoing acute respiratory disease pandemic termed COVID-19 caused by a newly emerged coronavirus has jeopardized the world’s health and economic sectors. As of 20 July 2020, the virus now known as SARS-CoV-2 has already infected more than 14 million individuals and killed 612,815 patients with a mortality rate of 4.12% around the world regardless of age, gender, and race. Main body Bangladesh has become one of its worst sufferers, with 207,453 infected people and 2668 related deaths with a mortality rate of 1.29% until 20 July 2020. More than 50% of COVID-19 patients in Bangladesh are aged between 21 and 40, but elderly people aged more than 60 have the highest mortality rate (44.7%). Male individuals are also more susceptible to the virus than females and consist of 71% and 79% among the infected and deceased patients, respectively. The most prevalent clinical features following the virus incubation period are fever, fatigue, and dry cough. A phylogenetic analysis study elucidated that the virus strain found in the country has 9 single-nucleotide variants, mostly in the ORF1ab gene, and a sequence containing 3 successive variants in the N protein, which reflects a weaker strain of SARS-CoV-2, implicating a possibility of its lower mortality rate. Another investigation of 184 genome samples of SARS-CoV-2 across the country implicated a close homology with a European haplotype of SARS-CoV-2. The country has also joined the race of vaccine development and started phase III clinical trials of a candidate vaccine developed by Sinovac Research and Development Co Ltd, China. Conclusion Bangladesh, as a developing country, still struggles with the pandemic and needs to scale up its response operation and improve healthcare facilities such as testing capacity, institutional quarantine, and isolation centers and promote awareness. Preventive measures such as strict lockdown, social distancing, and boosting the existing immune system are thus considered the only contrivances. </jats:sec

Mechanistic insight into the sensing of nitroaromatic compounds by metal-organic frameworks

There has been extensive research on the sensing of explosive nitroaromatic compounds (NACs) using fluorescent metal-organic frameworks (MOFs). However, ambiguity in the sensing mechanism has hampered the development of efficient explosive sensors. Here we report the synthesis of a hydroxyl-functionalized MOF for rapid and efficient sensing of NACs and examine in detail its fluorescence quenching mechanisms. In chloroform, quenching takes place primarily by exciton migration to the ground-state complex formed between the MOF and the analytes. A combination of hydrogen-bonding interactions and ??????? stacking interactions are responsible for fluorescence quenching, and this observation is supported by single-crystal structures. In water, the quenching mechanism shifts toward resonance energy transfer and photo-induced electron transfer, after exciton migration as in chloroform. This study provides insight into florescence-quenching mechanisms for the selective sensing of NACs and reduces the ambiguity regarding the nature of interactions between the MOF and NACs

Damping mechanisms for oscillations in solar prominences

Small amplitude oscillations are a commonly observed feature in prominences/filaments. These oscillations appear to be of local nature, are associated to the fine structure of prominence plasmas, and simultaneous flows and counterflows are also present. The existing observational evidence reveals that small amplitude oscillations, after excited, are damped in short spatial and temporal scales by some as yet not well determined physical mechanism(s). Commonly, these oscillations have been interpreted in terms of linear magnetohydrodynamic (MHD) waves, and this paper reviews the theoretical damping mechanisms that have been recently put forward in order to explain the observed attenuation scales. These mechanisms include thermal effects, through non-adiabatic processes, mass flows, resonant damping in non-uniform media, and partial ionization effects. The relevance of each mechanism is assessed by comparing the spatial and time scales produced by each of them with those obtained from observations. Also, the application of the latest theoretical results to perform prominence seismology is discussed, aiming to determine physical parameters in prominence plasmas that are difficult to measure by direct means.Comment: 36 pages, 16 figures, Space Science Reviews (accepted

Physics of Solar Prominences: II - Magnetic Structure and Dynamics

Observations and models of solar prominences are reviewed. We focus on non-eruptive prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and large-scale patterns of the filament channels in which prominences are located. Finally, several outstanding issues in prominence research are discussed, along with observations and models required to resolve them.Comment: 75 pages, 31 pictures, review pape