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A classical non-linear quasi-geostrophic model of wind-driven ocean circulation is integrated by using new additional boundary conditions conceived to: a) preserve, as far as possible, the typical structure of the Sverdrup flow in the southern and eastern regions of an idealised sub-tropical gyre and b) eliminate any additional boundary conditions in the northern and western regions of the fluid domain. Numerical simulations produce current and transport values close to those found in the literature whereas instability occurs at relatively low values of non-linearity, consistently with the well-known Sverdrup-like behaviour of large-scale transport in the world-wide ocean. A strict correlation emerges between the stability and the persistence of the Sverdrup-like behaviour of the so obtained solutions. [ABSTRACT FROM AUTHOR]

In the framework of stable free modes, a criterion is derived for the localisation in latitude of the intensified sector of the mode, i.e. northwards, southwards, or equally distributed in the north and south. The criterion is based on the sign taken by the inverse of the total vorticity at the middle latitude of the reference basin, and resorts to the necessarily westward orientation of an unforced current according to one of Greenspan's theorems. Some solutions, also of non-linear modes, elucidate the result. [ABSTRACT FROM AUTHOR]

Ierley's regional model of a single-gyre wind-driven circulation is an interesting compromise between the need to account for flow nonlinearity and its Sverdrupian behaviour far from the western area of the basin. The model assumes a priori that current intensification is westwards, but it can be easily reformulated, as the authors do, by setting the intensification region at the east. However, in this case the energetics of the flow exhibits an inconsistency that shows that westward intensification has no alternative. This is in accordance with all the previous conclusions on the subject but, for the first time, with the novelty of having taken into account also the nonlinear character of the flow outside the Sverdrupian area. [ABSTRACT FROM AUTHOR]

A new reading of westward intensification is put forward by decomposing the transport stream function in the sum of a couple of symmetric and anti-symmetric terms, relatively to the mirror reflection with respect to the central longitude of a reference basin, rectangular in shape and included into a certain beta plane. The consequence of the decomposition is twofold: first, the anti-symmetric term turns out to be a strict consequence of the latitudinal dependence of Coriolis acceleration, in the sense that it disappears in a hypothetical f-plane; second, whatever the wind forcing may be, the symmetric and anti-symmetric components of the meridional transport are always parallel in the western region of the basin and anti parallel in the eastern one. As a consequence of their superposition, the meridional transport is more energetic into the western region and it gives rise to the phenomenon of westward intensification. On the other hand, the components of the meridional transport tend to compensate each other in the eastern region in accordance with the Sverdrup balance. [ABSTRACT FROM AUTHOR]

The observed pseudoperiodic reversal of the upper-layer circulation of the Ionian Sea has been assumed to be related to some internal feedback processes (density driven) by the so-called BiOS (Adriatic-Ionian Bimodal Oscillating System) hypothesis. The idea behind this paper is that the Ionian circulation is driven by what happens in the boundary of the region, and so a very simple dynamical model has been derived by integrating in the bounded flow domain (the Ionian Basin) on the f-plane of the twolayer quasi-geostrophic evolution equations. Furthermore, a nonlinear term which mimics the mutual interaction between the moving layers has been introduced. By considering a stochastic Gaussian noise acting as a forcing and a decadal periodic input term having an amplitude much smaller than the noise variance, a stochastic resonance appears in the solution for a certain range of the values of the parameters. The decadal forcing at the boundary of the Ionian basin can be related to the lowfrequency atmospheric variability in the surrounding basins. The resonance has a period consistent with the observed decadal time scale of the reversal between cyclonic and anti-cyclonic phases. [ABSTRACT FROM AUTHOR]

Spike (S) glycoprotein is the largest structural protein of SARS-CoV-2 virus and the main one involved in anchoring of the host receptor ACE2 through the receptor binding domain (RBD). S protein secondary structure is of great interest for shedding light on various aspects, from functionality to pathogenesis, finally to spectral fingerprint for the design of optical biosensors. In this paper, the secondary structure of SARS-CoV-2 S protein and its constituting components, namely RBD, S1 and S2 regions, are investigated at serological pH by measuring their amide I infrared absorption bands through Attenuated Total Reflection Infrared (ATR-IR) spectroscopy. Experimental data in combination with MultiFOLD predictions, Define Secondary Structure of Proteins (DSSP) web server and Gravy value calculations, provide a comprehensive understanding of RBD, S1, S2, and S proteins in terms of their secondary structure content, conformational order, and interaction with the solvent., (© 2024 The Authors. Advanced Science published by Wiley‐VCH GmbH.)

All coronaviruses are characterized by spike glycoproteins whose S1 subunits contain the receptor binding domain (RBD). The RBD anchors the virus to the host cellular membrane to regulate the virus transmissibility and infectious process. Although the protein/receptor interaction mainly depends on the spike's conformation, particularly on its S1 unit, their secondary structures are poorly known. In this paper, the S1 conformation was investigated for MERS-CoV, SARS-CoV, and SARS-CoV-2 at serological pH by measuring their Amide I infrared absorption bands. The SARS-CoV-2 S1 secondary structure revealed a strong difference compared to those of MERS-CoV and SARS-CoV, with a significant presence of extended β-sheets. Furthermore, the conformation of the SARS-CoV-2 S1 showed a significant change by moving from serological pH to mild acidic and alkaline pH conditions. Both results suggest the capability of infrared spectroscopy to follow the secondary structure adaptation of the SARS-CoV-2 S1 to different environments.