17,735 research outputs found
A route to explain water anomalies from results on an aqueous solution of salt
In this paper we investigate the possibility to detect the hypothesized
liquid-liquid critical point of water in supercooled aqueous solutions of
salts. Molecular dynamics computer simulations are conducted on bulk TIP4P
water and on an aqueous solution of sodium chloride in TIP4P water, with
concentration c = 0.67 mol/kg. The liquid-liquid critical point is found both
in the bulk and in the solution. Its position in the thermodynamic plane shifts
to higher temperature and lower pressure for the solution. Comparison with
available experimental data allowed us to produce the phase diagrams of both
bulk water and the aqueous solution as measurable in experiments. Given the
position of the liquid-liquid critical point in the solution as obtained from
our simulations, the experimental determination of the hypothesized
liquid-liquid critical point of water in aqueous solutions of salts appears
possible.Comment: 5 pages, 6 figures. Accepted for publication on the Journal of
Chemical Physics (2010)
Structural Properties of High and Low Density Water in a Supercooled Aqueous Solution of Salt
We consider and compare the structural properties of bulk TIP4P water and of
a sodium chloride aqueous solution in TIP4P water with concentration c = 0.67
mol/kg, in the metastable supercooled region. In a previous paper [D.
Corradini, M. Rovere and P. Gallo, J. Chem. Phys. 132, 134508 (2010)] we found
in both systems the presence of a liquid-liquid critical point (LLCP). The LLCP
is believed to be the end point of the coexistence line between a high density
liquid (HDL) and a low density liquid (LDL) phase of water. In the present
paper we study the different features of water-water structure in HDL and LDL
both in bulk water and in the solution. We find that the ions are able to
modify the bulk LDL structure, rendering water-water structure more similar to
the bulk HDL case. By the study of the hydration structure in HDL and LDL, a
possible mechanism for the modification of the bulk LDL structure in the
solution is identified in the substitution of the oxygen by the chloride ion in
oxygen coordination shells.Comment: 10 pages, 10 figures, 2 tables. Accepted for publication on J. Phys.
Chem
Hodge polynomials of the moduli spaces of pairs
Let be a smooth projective curve of genus over the complex
numbers. A holomorphic pair on is a couple , where is a
holomorphic bundle over of rank and degree , and is
a holomorphic section. In this paper, we determine the Hodge polynomials of the
moduli spaces of rank 2 pairs, using the theory of mixed Hodge structures. We
also deal with the case in which has fixed determinant.Comment: 23 pages, typos added, minor change
Double dynamical regime of confined water
The Van Hove self correlation function of water confined in a silica pore is
calculated from Molecular Dynamics trajectories upon supercooling. At long time
in the relaxation region we found that the behaviour of the real space
time dependent correlators can be decomposed in a very slow, almost frozen,
dynamics due to the bound water close to the substrate and a faster dynamics of
the free water which resides far from the confining surface. For free water we
confirm the evidences of an approach to a crossover mode coupling transition,
previously found in Q space. In the short time region we found that the two
dynamical regimes are overimposed and cannot be distinguished. This shows that
the interplay between the slower and the faster dynamics emerges in going from
early times to the relaxation region, where a layer analysis of the
dynamical properties can be performed.Comment: 6 pages with 9 figures. RevTeX. Accepted for pulbication in J. Phys.
Cond. Mat
A Method for the Measurement of Digitizersâ Absolute Phase Error
A lot of engineering applications, from telecommunications to power systems, require
accurate measurement of phase angles. Some of them, like synchrophasor measurement and
calibration of instrument transformers with digital output, in order to reach high phase
measurement accuracy, require the knowledge of phase error of digitizers. Therefore, in this
paper a method for the measurement of digitizersâ absolute phase errors is proposed. It adopts a
sinewave and two square waves, that are the digitizer sample clock and a phase reference signal.
Combining the measurements of the relative phase differences between the adopted signals it is
possible to accurately evaluate the absolute phase error of a digitize
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