Climate impact on interannual variability of Weddell Sea Bottom Water

Bottom water formed in the Weddell Sea plays a significant role in ventilating the global abyssal ocean, forming a central component of the global overturning circulation. To place Weddell Sea Bottom Water in the context of larger scale climate fluctuations, we analyze the temporal variability of an 8‐year (April 1999 through January 2007) time series of bottom water temperature relative to the El Niño/Southern Oscillation (ENSO), Southern Annular Mode (SAM), and Antarctic Dipole (ADP). In addition to a pronounced seasonal cycle, the temperature record reveals clear interannual variability with anomalously cold pulses in 1999 and 2002 and no cold event in 2000. Correlations of the time series with ENSO, SAM, and ADP indices peak with the indices leading by 14–20 months. Secondary weaker correlations with the SAM index exist at 1–6 month lead time. A multivariate EOF analysis of surface variables shows that the leading mode represents characteristic traits of out‐of‐phase SAM and ENSO impact patterns and is well separated from other modes in terms of variance explained. The leading principal component correlates with the bottom water temperature at similar time scales as did the climate indices, implying impact from large‐scale climate. Two physical mechanisms could link the climate forcing to the bottom water variability. First, anomalous winds may alter production of dense shelf water by modulating open‐water area over the shelf. Second, surface winds may alter the volume of dense water exported from the shelf by governing the Weddell Gyre’s cyclonic vigor

Mechanical characteristics of groundnut shell particle reinforced polylactide nano fibre

ABSTRACT The PLA-groundnut shell solution is electrospun to produce nanocomposite fibre. The spinneret containing the composite solution was placed 24.7 cm away from the aluminium collector, tilted at an angle of 30 °, and the solution flow rate kept at 1 mL/min. Groundnut Shell particle (GSP) weight fraction used was varied from 3 - 8 wt. %. Particle reinforced nanofibres were formed on the collector from the composite solution at 26 kV. These nanofibres were subjected to tensile test and the result indicates that at 6 wt. % untreated GSP reinforced fibre possessed the best tensile stiffness of 24.62 MPa. This corresponds to 2.201 % increase in Modulus of Elasticity over the unreinforced PLA (1.07 MPa). The 7 wt. % treated GSP fibre showed the least stiffness (0.33 MPa), which is 69 % reduction over that of unreinforced fibre. PLA fibre reinforced with 5 wt. % untreated GSP displayed best blend of properties over the unreinforced with increase of 286 % (4.43 x 10-4 HB), 1,502 % (1.07 MPa), 286 % (0.22 MPa), 6.8 % (0.05 J) and 1,081 % (~ 0.15 MPa) in hardness, stiffness, UTS, energy at break and stress at break respectively. However, ductility decreased by ~33.3 % when compared to the unreinforced (18.27). The 5 wt. % untreated GSP PLA reinforced fibre showed the highest UTS (0.855 MPa). The micrographs showed beads on reinforced fibres, while the virgin PLA showed no beads

Driving β‑Strands into Fibrils

In this work we study contributions of mainchain and side chain atoms to fibrillization of polyalanine peptides using all-atom molecular dynamics simulations. We show that the total number of hydrogen bonds in the system does not change significantly during aggregation. This emerges from a compensatory mechanism where the formation of one interpeptide hydrogen bond requires rupture of two peptide–water bonds, leading to the formation of one extra water–water bond. Since hydrogen bonds are mostly electrostatic in nature, this mechanism implies that electrostatic energies related to these bonds are not minimized during fibril formation. Therefore, hydrogen bonds do not drive fibrillization in all-atom models. Nevertheless, they play an important role in this process since aggregation without the formation of interpeptide hydrogen bonds accounts for a prohibitively large electrostatic penalty (∼9.4 kJ/mol). Our work also highlights the importance of using accurate models to describe chemical bonds since Lennard-Jones and electrostatic contributions of different chemical groups of the protein and solvent are 1 order of magnitude larger than the overall enthalpy of the system. Thus, small errors in modeling these interactions can produce large errors in the total enthalpy of the system

Effects of Trimethylamine‑<i>N</i>‑oxide (TMAO) on Hydrophobic and Charged Interactions

Effects of trimethylamine-<i>N</i>-oxide (TMAO) on hydrophobic and charge–charge interactions are investigated using molecular dynamics simulations. Recently, these interactions in model peptides and in the Trp-Cage miniprotein have been reported to be strongly affected by TMAO. Neopentane dimers and Na⁺Cl^– are used, here, as models for hydrophobic and charge–charge interactions, respectively. Distance-dependent interactions, i.e., potential of mean force, are computed using an umbrella sampling protocol at different temperatures which allows us to determine enthalpy and entropic energies. We find that the large favorable entropic energy and the unfavorable enthalpy, which are characteristic of hydrophobic interactions, become smaller when TMAO is added to water. These changes account for a negligible effect and a stabilizing effect on the strength of hydrophobic interactions for simulations performed with Kast and Netz models of TMAO, respectively. Effects of TMAO on the enthalpy are mainly due to changes in terms of the potential energy involving solvent–solvent molecules. At the molecular level, TMAO is incorporated in the solvation shell of neopentane which may explain its effect on the enthalpy and entropic energy. Charge–charge interactions become stronger when TMAO is added to water because this osmolyte decreases the enthalpic penalty of bringing Na⁺ and Cl^– close together mainly by affecting ion–solvent interactions. TMAO is attracted to Na⁺, becoming part of its solvation shell, whereas it is excluded from the vicinity of Cl^–. These results are more pronounced for simulation performed with the Netz model which is more hydrophobic and has a larger dipole moment compared to the Kast model of TMAO