Supercritical water is fundamental in many fields of applications and a precise characterization of the supercritical state is of uttermost importance for this liquid. In a fluid, when moving from ...the critical point into the single-phase region, the thermodynamic response functions show maxima reminiscent of the critical divergence. Here we study the thermodynamic properties of water in the supercritical region by analysing both available experimental data and our computer simulation results. We find that the lines connecting the maxima of the response functions converge on approaching the critical point in a single line, the Widom line. We further show that the Widom line coincides with a crossover from a liquid-like to a gas-like behaviour clearly visible in the transport properties. These thermodynamic and dynamic features show that the supercritical state in water is far more complex than what was so far believed, indicating a new perspective in the characterization of the thermodynamics of this state.
Molecular dynamics simulations on the microsecond time scale have been performed on an aqueous solution of TIP4P/2005 water and NaCl by using the direct coexistence technique to study the ice growth ...and the ice/liquid interface water. At ambient pressure, for temperatures above the eutectic point of the salt and at seawater concentrations the brine rejection phenomenon and the spontaneous growth of an ice slab doped by the salt are obtained, as found in natural terrestrial and planetary environments. Experiments indicate that Cl
goes via substitution to ice sites. In line with this evidence we find a new result: the Cl
ion included in the lattice always substitutes not one but two water molecules, leaving the surrounding ice structure not distorted. The Na
ion shows a lower probability of being included in the ice and it occupies an interstitial site, causing a local distortion of the lattice. No signs of significant ion diffusion are observed in the lattice.
We present here molecular dynamics simulations of deeply supercooled SPC/E water confined in a cylindrical pore of MCM-41 silica material. By a layer analysis of the tag particle density correlators, ...we are able to extract the α-relaxation time of the mobile portion of the confined water. This relaxation time is the same as what can be extracted from neutron scattering experiments. From examination of the temperature-dependent behavior of the relaxation time and the dynamic susceptibility, we locate a dynamic crossover at T = (215 ± 5) K and a corresponding peak in the specific heat, in agreement with experimental findings in confined water and simulations of the bulk water. Our study demonstrates that the recent results of the experiments on confined water are extremely relevant for the comprehension of low-temperature bulk properties of water.
Molecular dynamics simulations have been performed on an aqueous solution of TIP4P/2005 water and NaCl using the direct coexistence technique to determine the equilibrium line ice/NaCl solution and ...the freezing point depression of water in presence of NaCl at different salt concentrations below the eutectic point. We used large samples in order to avoid finite size effects and to minimize the error on the determination of the freezing temperature. Our results are in excellent agreement with the experimental freezing point depression showing that the set of parameters used in this work for the water and NaCl is a very good choice to reproduce the thermodynamic properties of the water/NaCl system with molecular dynamics simulations.
•An exhaustive study by molecular dynamics to predict the water/NaCl phase equilibrium is presented.•At high salt concentrations, the rate of melting and freezing is slower due to the water-ion interactions.•Results presented at different salt contents obtained by simulation are in excellent agreement with the experimental data.•The freezing-point depression of water is an excellent test to validate the set of interaction parameters.•Direct coexistence is a very robust technique to estimate phase equilibria.
A very recent experimental paper importantly and unexpectedly showed that water in carbon nanotubes is already in the solid ordered phase at the temperature where bulk water boils. The water models ...used so far in literature for molecular dynamics simulations in carbon nanotubes show freezing temperatures lower than the experiments. We present here results from molecular dynamics simulations of water inside single walled carbon nanotubes using an extremely realistic model for both liquid and icy water, the TIP4P/ICE. The water behavior inside nanotubes of different diameters has been studied upon cooling along the isobars at ambient pressure starting from temperatures where water is in a liquid state. We studied the liquid/solid transition, and we observed freezing temperatures higher than in bulk water and that depend on the diameter of the nanotube. The maximum freezing temperature found is 390 K, which is in remarkable agreement with the recent experimental measurements. We have also analyzed the ice structure called “ice nanotube” that water forms inside the single walled carbon nanotubes when it freezes. The ice forms observed are in agreement with previous results obtained with different water models. A novel finding, a partial proton ordering, is evidenced in our ice nanotubes at finite temperature.
Direct coexistence simulations on a microsecond time scale have been performed for different types of ice (Ih, Ic, III, V, and VI) in contact with a NaCl aqueous solution at different pressures. In ...line with the previous results obtained for ice Ih Conde et al., Phys. Chem. Chem. Phys., 2017, 19, 9566–9574, our results reveal the spontaneous growth of a new ice doped phase and the formation of a brine rejection phase in all ices studied. However, both the preferential incorporation of ions into the ice lattice and the inclusion mechanisms depend on the crystalline structure of each ice. This work shows the inclusion of Cl− and Na+ ions in ice from salt using molecular dynamics simulation, in agreement with the experimental evidence found in the literature. The model used for water is TIP4P/2005. For NaCl we employ a set of potential parameters that uses unit charges for the ions.
The Data Quality Monitoring (DQM) Software is a central tool in the CMS experiment. Its flexibility allows for integration in several key environments: Online, for real-time detector monitoring; ...Offline, for the final, fine-grained data analysis and certification; Release-Validation, to constantly validate the functionality and the performance of the reconstruction software; in Monte Carlo productions. Since the end of data taking at a center of mass energy of 8 TeV, the environment in which the DQM lives has undergone fundamental changes. In turn, the DQM system has made significant upgrades in many areas to respond to not only the changes in infrastructure, but also the growing specialized needs of the collaboration with an emphasis on more sophisticated methods for evaluating data quality, as well as advancing the DQM system to provide quality assessments of various Monte Carlo simulations versus data distributions, monitoring changes in physical effects due to modifications of algorithms or framework, and enabling regression modeling for long-term effects for the CMS detector. The central tool to deliver Data Quality information is an interactive web site for browsing data quality histograms (DQMGUI). In this contribution the usage of the DQM Software in the different environments and its integration in the CMS Reconstruction Software Framework (CMSSW) and in all production workflows are presented, with emphasis on recent developments and improvement in advance of the LHC restart at 13 TeV. The main technical challenges and the adopted solutions to them will be also discussed with emphasis on functionality and long-term robustness.
The CMS tracking code is organized in several levels, known as iterative steps, each optimized to reconstruct a class of particle trajectories, as the ones of particles originating from the primary ...vertex or displaced tracks from particles resulting from secondary vertices. Each iterative step consists of seeding, pattern recognition and fitting by a kalman filter, and a final filtering and cleaning. Each subsequent step works on hits not yet associated to a reconstructed particle trajectory. The CMS tracking code is continuously evolving to make the reconstruction computing load compatible with the increasing instantaneous luminosity of LHC, resulting in a large number of primary vertices and tracks per bunch crossing. The major upgrade put in place during the present LHC Long Shutdown will allow the tracking code to comply with the conditions expected during RunII and the much larger pileup. In particular, new algorithms that are intrinsically more robust in high occupancy conditions were developed, iterations were re-designed (including new ones, dedicated to specific physics objects), code optimizations were deployed and new software techniques were used. The speed improvement has been achieved without significant reduction in term of physics performance. The methods and the results are presented and the prospects for future applications are discussed.
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