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Upwinding allows for accurate, non-oscillatory capturing of shocks waves; however, many Riemann solvers (both exact and approximate) suffer from some sort of numerical instability. One of the most mysterious and least understood of these is the carbuncle phenomenon. In the present study, we analyse the closely allied ''simplified carbuncle'' problem, also known as the 2D shock stability problem or the 1.5D carbuncle problem. Motivated by the existence of some recently derived schemes that do not exhibit the instability, we perform a thorough stability analysis and extend previous studies by analysing the pseudo-spectra and hence the effects of non-normality in causing this instability. Our results establish that, contrary to previous indications in the literature, a non-linear mechanism is responsible for the instability. In order to understand the nature of this non-linear mechanism better, we perform a non-linear analysis of the sonic glitch, which shares some common features with the carbuncle. We provide two previously unknown results. Firstly, we show that even the ''entropy-satisfying'' Godunov scheme violates the entropy condition in the sonic glitch. Secondly, we provide a more accurate definition for the entropy condition for scalar conservation laws that supports the previous claim. We conjecture that a similar non-linear anti-dissipative mechanism might be responsible in triggering the carbuncle. This work is expected to lead to a better understanding of possible unphysical behaviour in Riemann solvers and thus help in the design of better solvers for high-Reynolds-number flows.

Introduction: The objective of the study was to determine T-cell subtypes, Natural Killer cell activity and cytokines in COVID-19 patients with mild to moderate disease and compare them between patients who had recovered and those who had progressed to severe disease. Methods: Peripheral blood samples of COVID-19 patients were collected at the time of hospital admission and after one week. These samples were analysed for interleukins (IL-6, IL-17a) using chemiluminescence ELISA. The T-cell subsets (T naïve, T regulatory, Th17, Th1, Th2, CD8+ T cells] were studied using flow cytometry. Mild, moderate and severe COVID-19 are defined as per CDC guidelines. Results: Nineteen COVID-19-positive patients were enrolled between June 2020 to December 2021. Nine had mild COVID-19 and 10 had moderate COVID-19 at recruitment. All mild cases recovered without progression to severe disease, while five patients from the moderate group progressed to severe disease. Overall, there is a decrease in lymphocyte count in patients with moderate-severe disease, but the ratio of Th17 [5.91 (2.69-12.01)] was higher compared to Th1 [1.12 (0.27-3.13)] and Th2[2.34 (2-3.5)]. The high baseline level of IL-6 observed in patients with moderate disease leads to the proliferation of more Th17 type of CD4+ T-cells(p=0.002) and suppression of Treg cells. A higher Th17 subset leads to neutrophilic inflammation in patients with severe COVID-19. Conclusion: Interpretation & conclusions: Higher baseline IL-6 leads to depletion of regulatory T-cells, Th1 & Th2 CD4 cells. IL-6 leads to the proliferation of Th17 type of CD4+ subsets in moderate COVID-19. Higher Th17 cells in moderate COVID-19 patients lead to the production of IL-17a, which may result in intense neutrophilic inflammatory response and cytokine storm.

Optic pathway gliomas(OPG) are low-grade neoplasms arising from the pre-cortical optic pathways. OPG can involve the optic nerve,optic chiasm,optic tracts,optic radiations,or the hypothalamus.Most commonly affecting children,they present usually with headache and vision related complaints .In this,we describe the a rare case of optic glioma presenting with limb weakness and role of MRI in it's diagnosis