227 research outputs found
A New Global Ocean Climatology
A new global ocean temperature and salinity climatology is proposed for two time periods: a long time mean using multiple sensor data for the 1900–2017 period and a shorter time mean using only profiling float data for the 2003–2017 period. We use the historical database of World Ocean Database 2018. The estimation approach is novel as an additional quality control procedure is implemented, along with a new mapping algorithm based on Data Interpolating Variational Analysis. The new procedure, in addition to the traditional quality control approach, resulted in low sensitivity in terms of the first guess field choice. The roughness index and the root mean square of residuals are new indices applied to the selection of the free mapping parameters along with sensitivity experiments. Overall, the new estimates were consistent with previous climatologies, but several differences were found. The cause of these discrepancies is difficult to identify due to several differences in the procedures. To minimise these uncertainties, a multi-model ensemble mean is proposed as the least uncertain estimate of the global ocean temperature and salinity climatology
On the nature of long-range contributions to pair interactions between charged colloids in two dimensions
We perform a detailed analysis of solutions of the inverse problem applied to
experimentally measured two-dimensional radial distribution functions for
highly charged latex dispersions. The experiments are carried out at high
colloidal densities and under low-salt conditions. At the highest studied
densities, the extracted effective pair potentials contain long-range
attractive part. At the same time, we find that for the best distribution
functions available the range of stability of the solutions is limited by the
nearest neighbour distance between the colloidal particles. Moreover, the
measured pair distribution functions can be explained by purely repulsive pair
potentials contained in the stable part of the solution.Comment: 6 pages, 5 figure
NMR investigations of interactions between anesthetics and lipid bilayers
Interactions between anesthetics (lidocaine and short chain alcohols) and lipid membranes formed by dimyristoylphosphatidylcholine (DMPC) were studied using NMR spectroscopy. The orientational order of lidocaine was investigated using deuterium NMR on a selectively labelled compound whereas segmental ordering in the lipids was probed by two-dimensional 1H-13C separated local field experiments under magic-angle spinning conditions. In addition, trajectories generated in molecular dynamics (MD) computer simulations were used for interpretation of the experimental results. Separate simulations were carried out with charged and uncharged lidocaine molecules. Reasonable agreement between experimental dipolar interactions and the calculated counterparts was observed. Our results clearly show that charged lidocaine affects significantly the lipid headgroup. In particular the ordering of the lipids is increased accompanied by drastic changes in the orientation of the P-N vector in the choline group
Operational evaluation of the Mediterranean Monitoring and Forecasting Centre products: implementation and results
A web-based validation platform has been developed at the Istituto Nazionale di Geofisica e Vulcanologia (INGV) for the Near Real Time validation of the MyOcean-Mediterranean Monitoring and Forecasting Centre products (Med-MFC). A network for the collection of the in-situ observations, the nested sub-basin forecasting systems model data (provided by the partners of the Mediterranean Operational Oceanography Network, MOON) and the Sea Surface Temperature (SST) satellite data has been developed and is updated every day with the new available data. The network collects temperature, salinity, currents and sea level data. The validation of the biogeochemical forecast products is done by use of ocean colour satellite data produced for the Mediterranean Sea. All the data are organized in an ad hoc database interfaced with a dedicated software which allows interactive visualizations and statistics (CalVal SW). This tool allows to evaluate NRT products by comparison with independent observations for the first time. The heterogeneous distribution and the scarcity of moored observations reflect with large areas uncovered with measurements. Nevertheless, the evaluation of the forecast at the locations of observations could be very useful to discover sub-regions where the model performances can be improved, thus yielding an important complement to the basin-mean statistics regularly calculated for the Mediterranean MFC products using semi-independent observations
Mediterranean Sea large-scale low-frequency ocean variability and water mass formation rates from 1987 to 2007: A retrospective analysis
We describe a synthesis of the Mediterranean Sea circulation structure and dynamics from a 23-year- long reanalysis of the ocean circulation carried out by Adani et al. (2011). This mesoscale permitting dynamical reconstruction of past ocean variability in the Mediterranean Sea allows the study of the time-mean circulation and its low frequency, decadal, components. It is found that the time-mean circu- lation is composed of boundary and open ocean intensified jets at the border of cyclonic and anticyclonic gyres. The large scale basin circulation is generally characterized in the northern regions by cyclonic gyres and in its southern parts by anticyclonic gyres and eddy-dominated flow fields, with the exception of the Tyrrhenian and the northern Ionian Sea. The time-mean Tyrrhenian Sea circulation is dominated by cyclonic gyres of different intensity and intermittency. The northern Ionian Sea circulation, however, reverses in sign in two ten-year periods, the first in 1987–1996 and the second in 1997–2006, which is here called the Northern Ionian reversal phenomenon. This reversal is provoked by the excursion of the Atlantic-Ionian Stream from the middle to the northern parts of the basin. The decadal variability of other parts of the basin is characterized by changes in strength of the basin scale structures. The water mass formation rates and variability are dominated by event-like periods where the intermediate and deep waters are formed for 2–3 years at higher rates. The largest deep water formation events of the past 23 years occurred separately in the western and eastern Mediterranean basin: the first coincided with the Eastern Mediterranean Transient (Roether et al., 1996) and the second with the western Mediterranean deep water formation event in 2005–2006 (Smith et al., 2008). A new schematic of the basin-scale circu- lation is formulated and commented.Published318-3324A. Oceanografia e climaJCR Journa
Attraction between DNA molecules mediated by multivalent ions
The effective force between two parallel DNA molecules is calculated as a
function of their mutual separation for different valencies of counter- and
salt ions and different salt concentrations. Computer simulations of the
primitive model are used and the shape of the DNA molecules is accurately
modelled using different geometrical shapes. We find that multivalent ions
induce a significant attraction between the DNA molecules whose strength can be
tuned by the averaged valency of the ions. The physical origin of the
attraction is traced back either to electrostatics or to entropic
contributions. For multivalent counter- and monovalent salt ions, we find a
salt-induced stabilization effect: the force is first attractive but gets
repulsive for increasing salt concentration. Furthermore, we show that the
multivalent-ion-induced attraction does not necessarily correlate with DNA
overcharging.Comment: 51 pages and 13 figure
Hydration interactions: aqueous solvent effects in electric double layers
A model for ionic solutions with an attractive short-range pair interaction
between the ions is presented. The short-range interaction is accounted for by
adding a quadratic non-local term to the Poisson-Boltzmann free energy. The
model is used to study solvent effects in a planar electric double layer. The
counter-ion density is found to increase near the charged surface, as compared
with the Poisson-Boltzmann theory, and to decrease at larger distances. The ion
density profile is studied analytically in the case where the ion distribution
near the plate is dominated only by counter-ions. Further away from the plate
the density distribution can be described using a Poisson-Boltzmann theory with
an effective surface charge that is smaller than the actual one.Comment: 11 Figures in 13 files + LaTex file. 20 pages. Accepted to Phys. Rev.
E. Corrected typos and reference
Temperature and density extrapolations in canonical ensemble Monte Carlo simulations
We show how to use the multiple histogram method to combine canonical
ensemble Monte Carlo simulations made at different temperatures and densities.
The method can be applied to study systems of particles with arbitrary
interaction potential and to compute the thermodynamic properties over a range
of temperatures and densities. The calculation of the Helmholtz free energy
relative to some thermodynamic reference state enables us to study phase
coexistence properties. We test the method on the Lennard-Jones fluids for
which many results are available.Comment: 5 pages, 3 figure
The osmotic pressure of charged colloidal suspensions: A unified approach to linearized Poisson-Boltzmann theory
We study theoretically the osmotic pressure of a suspension of charged
objects (e.g., colloids, polyelectrolytes, clay platelets, etc.) dialyzed
against an electrolyte solution using the cell model and linear
Poisson-Boltzmann (PB) theory. From the volume derivative of the grand
potential functional of linear theory we obtain two novel expressions for the
osmotic pressure in terms of the potential- or ion-profiles, neither of which
coincides with the expression known from nonlinear PB theory, namely, the
density of microions at the cell boundary. We show that the range of validity
of linearization depends strongly on the linearization point and proof that
expansion about the selfconsistently determined average potential is optimal in
several respects. For instance, screening inside the suspension is
automatically described by the actual ionic strength, resulting in the correct
asymptotics at high colloid concentration. Together with the analytical
solution of the linear PB equation for cell models of arbitrary dimension and
electrolyte composition explicit and very general formulas for the osmotic
pressure ensue. A comparison with nonlinear PB theory is provided. Our analysis
also shows that whether or not linear theory predicts a phase separation
depends crucially on the precise definition of the pressure, showing that an
improper choice could predict an artificial phase separation in systems as
important as DNA in physiological salt solution.Comment: 16 pages, 5 figures, REVTeX4 styl
Observational Evidence of the Basin-Wide Gyre Reversal in the Gulf of Taranto
The paper shows for the first time the observational evidence of basin-wide gyre reversal in the Gulf of Taranto (north-western Ionian Sea in the eastern Mediterranean Sea) by means of two specifically designed in situ oceanographic campaigns (based on CTD and ADCP measurements). The analysis of the in situ data shows a change in circulation from anticyclonic in October 2014 to cyclonic in June\u2013July 2016. Furthermore, long-term (1993\u20132018) analysis using gridded satellite altimetry data in the Gulf of Taranto shows that the cyclonic gyres are more frequent than anticyclonic gyres. The latter occur only for 2 to 3 years at a time in some decades
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