10,259 research outputs found
Molecular dynamics study of the glass transition in confined water
A molecular dynamics simulation of SPC/E water confined in a Silica pore is
presented. The pore has been constructed to reproduce the average properties of
a pore of Vycor glass. Due to the confinement and to the presence of a strong
hydrophilic surface, the dynamic behaviour of the liquid appears to be strongly
dependent on the hydration level. The approach to the glass transition of
confined water is investigated on lowering hydration and on supercooling in the
framework of Mode Coupling Theories. At higher hydrations two quite distinct
subsets of water molecules are detectable. Those belonging to the first layer
close to the substrate suffer a severe slowing down, while the remaining ones
display a scenario typical of supercooled liquids approaching the kinetic glass
transition.Comment: Talk presented at "International Workshop on Dynamics in
Confinement", Grenoble January 2000, to be appear in J. Phys. Franc
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)
Local order in aqueous solutions of rare gases and the role of the solute concentration: a computer simulation study with a polarizable potential
Aqueous solutions of rare gases are studied by computer simulation employing
a polarizable potential for both water and solutes. The use of a polarizable
potential allows to study the systems from ambient to supercritical conditions
for water. In particular the effects of increasing the concentration and the
size of the apolar solutes are considered in an extended range of temperatures.
By comparing the results at increasing temperature it appears clearly the
change of behaviour from the tendency to demix at ambient conditions to a
regime of complete solubility in the supercritical region. In this respect the
role of the hydrogen bond network of water is evidenced.Comment: Accepted for publication in Molecular Physics 2004. 19 pages, 10
figure
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
Systemic risk in a mean-field model of interbank lending with self-exciting shocks
In this paper we consider a mean-field model of interacting diffusions for
the monetary reserves in which the reserves are subjected to a self- and
cross-exciting shock. This is motivated by the financial acceleration and fire
sales observed in the market. We derive a mean-field limit using a weak
convergence analysis and find an explicit measure-valued process associated
with a large interbanking system. We define systemic risk indicators and
derive, using the limiting process, several law of large numbers results and
verify these numerically. We conclude that self-exciting shocks increase the
systemic risk in the network and their presence in interbank networks should
not be ignored
Systemic risk in a mean-field model of interbank lending with self-exciting shocks
In this paper we consider a mean-field model of interacting diffusions for
the monetary reserves in which the reserves are subjected to a self- and
cross-exciting shock. This is motivated by the financial acceleration and fire
sales observed in the market. We derive a mean-field limit using a weak
convergence analysis and find an explicit measure-valued process associated
with a large interbanking system. We define systemic risk indicators and
derive, using the limiting process, several law of large numbers results and
verify these numerically. We conclude that self-exciting shocks increase the
systemic risk in the network and their presence in interbank networks should
not be ignored
The untapped potential of plant thin cell layers
Thin cell layers (TCLs), which contain a small number of cells or tissues, are explants excised from different organs (stems, leaves, roots, inflorescences, flowers, cotyledons, hypocotyls/epicotyls, and embryos). After almost 45 years of research, this culture system has been used for several monocotyledonous and dicotyledonous plants of commercial importance, and for model plants. The limited amount of cells in a TCL is of paramount importance because marker molecules/genes of differentiation can be easily localized in situ in the target/responsive cells. Thus, the use of TCLs has allowed, and continues to allow, for the expansion of knowledge in plant research in a practical and applied manner into the fields of tissue culture and micropropagation, cell and organ genetics, molecular biology, biochemistry, and development. Starting from a brief historical background, the actual and potential uses of the TCL system are briefly reviewed
Computer simulation of the phase diagram for a fluid confined in a fractal and disordered porous material
We present a grand canonical Monte Carlo simulation study of the phase
diagram of a Lennard-Jones fluid adsorbed in a fractal and highly porous
aerogel. The gel environment is generated from an off-lattice diffusion limited
cluster-cluster aggregation process. Simulations have been performed with the
multicanonical ensemble sampling technique. The biased sampling function has
been obtained by histogram reweighting calculations. Comparing the confined and
the bulk system liquid-vapor coexistence curves we observe a decrease of both
the critical temperature and density in qualitative agreement with experiments
and other Monte Carlo studies on Lennard-Jones fluids confined in random
matrices of spheres. At variance with these numerical studies we do not observe
upon confinement a peak on the liquid side of the coexistence curve associated
with a liquid-liquid phase coexistence. In our case only a shouldering of the
coexistence curve appears upon confinement. This shoulder can be associated
with high density fluctuations in the liquid phase. The coexisting vapor and
liquid phases in our system show a high degree of spatial disorder and
inhomogeneity.Comment: 8 pages, 8 figures, to be published in Phys. Rev.
Non-strategic nuclear weapons: the next step in multilateral arms control
This paper by Crispin Rovere and Kalman A Robertson addresses the many barriers to including tactical nuclear weapons in disarmament talks. It considers the difficulty of bringing other emerging powers such as China into the nuclear arms control equation.
The study proposes a new arms control treaty that would ban outright the development and possession of a special kind of tactical nuclear weapon called \u27low-yield nuclear weapons\u27 that the authors argue carries an increasingly grave risk of starting a nuclear war.
The paper says that Australia should take the lead in promoting a new treaty banning low-yield nuclear weapons.
A longer discussion paper, which includes a more thorough exploration of the technical, strategic and legal issues, as well as many references for further reading is available below
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