Publications (26)28.76 Total impact
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ABSTRACT: Simulations of ices III and V are performed using molecular dynamics calculations in the NPT ensemble. To represent molecular interactions in both ices, two potentials, TIP4P and TIP5P, are used. The specific volume of ice III is calculated as a function of temperature at pressure P = 250 MPa, as well as a function of pressure at temperature T = 246 K. For ice V, the specific volume is calculated as a function of temperature at P = 500 MPa and as a function of pressure at T = 238 K. In both cases, both TIP4P and TIP5P models are used. The results of the calculations are in good agreement with the experimental data of other researchers. 
Conference Paper: Thermodynamic properties of highpressure ices: A review
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ABSTRACT: Being one of the most interesting compounds in the universe, water substance possesses a large number of wellestablished solidstate polymorphs commonly known as ices, along with liquid, vapor and amorphous phases. Thermodynamics of ices and their equations of state are of fundamental importance for such areas of science and technology as oceanography, space and planetary science, glaciology, physics of shock compression of water substance, highpressure food processing and lowtemperature preservation of biological materials. In general terms, a complete thermodynamic description of a substance is afforded by the knowledge of its PVT equation of state and the knowledge of the specific heat capacity Cp along some curve on the temperaturepressure diagram not an isothermal. This presentation will give an overview of the stateoftheart and the ongoing research on the PVT equations of state of highpressure ices, as well as experimental data and the results of molecular dynamics and Monte Carlo computer simulations used to derive them. PVT equations of state of ices II, III, V, VI, VII and VIII will be presented. Experimental data on the specific heat capacity Cp of highpressure ices are rather limited. A method of evaluation of Cp based on the thermodynamic relationship for the ‘jumps‘ of the specific heat capacity of ices across the transition lines will be discussed. The highly precise analytical formulation for liquid water and vapor, IAPWS95, in the form of a Helmholtz potential, and a recent IAPWS Release 2006 for ice Ih in the form of a Gibbs potential function describe thermodynamic properties of water and ice in a consistent manner and permit very accurate numerical simulations of equilibrium and nonequilibrium phenomena. No such fundamental equations of state have been proposed so far for highpressure ices. A possible strategy to achieve this goal will also be discussed in the presentation.  [Show abstract] [Hide abstract]
ABSTRACT: A new equation of state of ice Ih recently proposed by Feistel and Wagner [J. Phys. Chem. Ref. Data 35 (2006) 1021–1047] is used to study the phenomena related to the equilibrium isentropic compression of an ice–water mixture and dynamic loading of solid ice. New results are presented concerning the properties of the new equation of state, equilibrium solid–liquid phase transitions and Hugoniots of lowtemperature (100K) and temperate (263K) shockcompressed ice.  [Show abstract] [Hide abstract]
ABSTRACT: Numerous data indicate discernible warming of the Northern Hemisphere in the 20th century especially at high latitudes. Summer melting at the surface of Arctic glaciers is likely to increase this warming. To verify this phenomenon, we reconstruct the past temperatures of the Arctic ice caps at their surface and at the 10 m depth. The reconstructions are made for two Arctic ice caps (Austfonna and Akademii Nauk) by means of the inversion of the measured temperaturedepth profiles. In addition, we use the measured oxygen–isotope ratio and the melt feature index as input data. We find that the present ice temperature is the highest over the last 1000 years, while the lowest temperature occurred in the 1700s. The surface temperature variations of Akademii Nauk (Severnaya Zemlya) and Austfonna (Svalbard) Ice Caps exceed the average Arctic temperature anomalies over the last 150 years by 6 to 7 °C.  [Show abstract] [Hide abstract]
ABSTRACT: The formation of high concentrations of contaminants in Mexico City's atmosphere due to the vehicular transit constitutes an acute problem. Based on that, and before alternative fuels are proposed for clean use, it is widely justified to evaluate the environmental impact these may have as a source of pollution. As the liquefied petroleum gas mix used as a domestic fuel has been proposed alternatively for motor cars, we present here a simulation study of the photochemical smog formation driven by nbutane via two different reaction schemes. In the first one (Mechanism A), the reaction takes place through the hydroxyl radical, (.)OH, attack on ail nbutane secondarycarbonhydrogen in the absence or presence of carbonylic compounds. No significant nbutane consumption or ozone formation was found. The second scheme (Mechanism B) which we hypothesise will occur in the presence of carbonylic compounds goes via the (.)OH attack oil ail nbutane primarycarbonhydrogen, led to some nbutane consumption and high ozone concentrations.  [Show abstract] [Hide abstract]
ABSTRACT: The 2004 Gibbs thermodynamic potential function of naturally abundant water ice is based on much more experimental data than its predecessors, is therefore significantly more accurate and reliable, and for the first time describes the entire temperature and pressure range of existence of this ice phase. It is expressed in the ITS90 temperature scale and is consistent with the current scientific pure water standard, IAPWS95, and the 2003 Gibbs potential of seawater. The combination of these formulations provides sublimation pressures, freezing points, and sea ice properties covering the parameter ranges of oceanographic interest. This paper provides source code examples in Visual Basic, Fortran and C++ for the computation of the Gibbs function of ice and its partial derivatives. It reports the most important related thermodynamic equations for ice and sea ice properties.  [Show abstract] [Hide abstract]
ABSTRACT: New PVT EOS of ices III and V have been derived [1], as well as new isothermal EOS of ices VII and VIII. MD simulations have been carried out to calculate the densities of ices III, V and VIII as functions of pressure and temperature; the TIP4P and TIP5P models have been adopted. A scheme [2] for calculating the heat capacity of ices II, III, V, VI, and VII has been applied. Recently developed new Gibbs thermodynamic potential function of ice Ih [3] has been used to calculate the 100 K Hugoniot of ice for pressures up to 0.5 GPa; the results are in good agreement with experimental data of Stewart [4]. The validity of the existing EOS of liquid water in the metastable region at high pressures has also been investigated. The IAPWS95 Formulation was found to be the only EOS of liquid water valid in the lowtemperature metastable region both at low and at very high pressures. [1] V. Tchijov, R. Baltazar Ayala, G. Cruz Leon, O. Nagornov, J. Phys. Chem. Solids 65, 1277 (2004). [2] V. Tchijov, J. Phys. Chem. Solids 65, 851 (2004). [3] R. Feistel, W. Wagner, J. Mar. Res. (2005, in press). [4] S. T. Stewart, PhD Thesis, California Institute of Technology (2002).  [Show abstract] [Hide abstract]
ABSTRACT: A theoretical analysis of the growth probability measure as well as multifractal dimensions and maximum (minimum) growth probability in the socalled bicolored diffusion limited aggregation (BDLA) model is presented. This model deals with the competing growth of two colored immobile fractal clusters. 
Article: Reconstruction of past temperatures for Arctic glaciers subjected to intense subsurface melting
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ABSTRACT: Many glaciers are subject to melting due to high summer air temperatures. Here, the presence of meltwater in the subsurface layers of the glacier bulk, and its subsequent percolation and refreezing are implemented in the calibration of a paleothermometer. Accounting for the melt feature index and the measured oxygenisotope ratio allows for calibration of the paleothermometer and comparison of different climatic proxies. The results of reconstructions agree with previous reconstructions at the depth of attenuation of the seasonal climate signals, which supports the validity of the paleothermometer calibration. The sensitivity of the reconstruction to variations of the model parameters was also studied. It was found that most likely snowfirn sequence and temperature fields were subjected to significant change due to current warming. Temperature changes in the snowfirn thickness of Akademii Nauk (Severnaya Zemlya, Russian High Arctic) and Austfonna (Svalbard) ice caps exceed by ∼6°C the average Arctic temperature anomalies for the last 150 years. The reconstruction of the past surface temperatures and the parameters of the subsurface heat source due to refreezing of meltwater lead to the conclusion that meltwater spreads inside two to four annual layers for Akademii Nauk and Austfonna ice caps, respectively.  [Show abstract] [Hide abstract]
ABSTRACT: Thermodynamic properties of highpressure ice polymorphs, ices III and V, are studied theoretically. The results of TIP4P molecular dynamics simulations in the NPT ensemble are used to calculate the temperature dependence of the specific volume of ices III and V at pressures 0.25 and 0.5 GPa, respectively. New PVT equations of state of ices III and V are derived using a method generalizing the one proposed by Fei et al. [J. Chem. Phys. 99 (1993) 5369], and new results concerning the equilibrium phase transitions ice IIIwater and ice Vwater are presented.  [Show abstract] [Hide abstract]
ABSTRACT: The isobaric heat capacity CP of highpressure water ice polymorphs (ices III, V, VI, and VII) is calculated using P–V–T equations of state of ices, jump condition for CP on the lines of phase transition, and the equations of the lines of phase transition on the P–T diagram of water substance.  [Show abstract] [Hide abstract]
ABSTRACT: New PVT EOS of highpressure ices II, III, V, VI, and VII are derived by applying a method generalizing the one proposed by Fei et al. For ices III and V, molecular dynamics simulations are carried out to calculate their densities as functions of temperature using TIP4P and TIP5P water models [1]. A novel scheme for calculating the heat capacity of ices II, III, V, VI, and VII is proposed [2]. Equilibrium phase transitions between H_2O phases are studied using the derived EOS and the calculated thermodynamic quantities of highpressure ices. The lines of phase changes on the PT diagram and the phase boundaries on the PV diagram are computed; the results are in very good agreement with experimental data. The application to multiple nonequilibrium phase transitions in ice subjected to shockwave compression [3] will be discussed, as well as the validity of the existing EOS of liquid water in the metastable region at high pressures. [1] R. Baltazar Ayala, V. Tchijov, Can. J. Phys. 81, 11 (2003). [2] V. Tchijov, J. Phys. Chem. Solids (2004, in press). [3] G. Cruz León et al., Entropie No. 239/240, 66 (2002).  [Show abstract] [Hide abstract]
ABSTRACT: Thermodynamic properties of highpressure solid phase ice II are studied theoretically. The P–V–T equation of state of ice II is derived and its thermodynamic functions are calculated based on the available experimental data. New results are presented concerning the equilibrium solid–solid phase transitions between ice II and ice Ih, ice II and III, and ice II and V.  [Show abstract] [Hide abstract]
ABSTRACT: We analyze the existing equationsofstate of liquid water from the point of view of their applicability to equilibrium and nonequilibrium waterice phase change problems that involve supercooled water. We show that the equationofstate of Saul and Wagner [J. Phys. Chem. Ref. Data 18, 1537 (1989)] is most suitable for the description of thermodynamic properties of supercooled water in the range of pressures 0200 kbar, and find the area of its validity in the metastable region. 
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ABSTRACT: Experiments indicate that water ice subjected to shockwave loading undergoes multiple nonequilibrium phase transitions (Larson D.B., J. Glaciology, 30:235, 1984.) Kinetic model of multiple phase changes in ice (Tchijov V. et al., J. Phys. Chem., 101:6215, 1997) is based on the complete set of PVT equations of state of ices Ih, III, V, VI, VII and liquid water in the ranges of pressure 0..40 kbar and temperature 230..500 K. Detailed study of thermodynamic properties of ice phases including the derivation of the equations of state and investigation of the isoentropes of binary liquidsolid and solidsolid mixtures is presented. The shapes of the isoentropes suggest the unusually complicated nature of phase changes in ice. In the kinetic model, a set of parameters is introduced that permits to describe the loading and unloading paths and hysteresis on the PV diagram of nonequilibrium mixture of ice phases. The proposed kinetic model is applied to study the propagation of onedimensional compression wave in an ice sample. The results of computer simulations are in good agreement with the existing experimental data.  [Show abstract] [Hide abstract]
ABSTRACT: Experimental studies of shockwave loading of ice (D.B. Larson, J. Glaciol., 1984, Vol.30, p.235) indicate multiple solidsolid and solidliquid phase transitions. In order to model these phase changes, we develop a complete set of the PVT equations of state of ices Ih, II, III, V, VI, and VII. We study the isoentropes of icewater mixture along the lines of solidliquid phase transitions on the PT diagram, with special attention to highpressure ice VII  water transition where various PVT equations of liquid water are used and compared. A kinetic model of multiple phase transitions in ice in the pressure range 02000 MPa has been reported elsewhere (V. Tchijov et al., J. Phys. Chem. B, 1997, Vol.101, p.6215). We use this model, extended to include ice VII, to investigate the loading and unloading paths and the hysteresis on the PV diagram of ice in the pressure range 03600 MPa. We compare the results of our computer simulations against available experimental data.  [Show abstract] [Hide abstract]
ABSTRACT: Random walks with nearest neighbors prohibited, of lengths N up to 1024 steps, are studied on the threedimensional diamond lattice. This is a model to describe steric effects given by geometrical constraints on the conformation of macromolecules. Short walks (N  [Show abstract] [Hide abstract]
ABSTRACT: We study the distribution of the endtoend distance of continuoustime selfavoiding random walks (CTRW) in dimension four from two viewpoints. From a realspace renormalizationgroup map on probabilities, we conjecture the asymptotic behavior of the endtoend distance of a weakly selfavoiding random walk (SARW) that penalizes twobody interactions of random walks in dimension four on a hierarchical lattice. Then we perform the Monte Carlo computer simulations of CTRW on the fourdimensional integer lattice, paying special attention to the difference in statistical behavior of the CTRW compared with the discretetime random walks. In this framework, we verify the result already predicted by the renormalizationgroup method and provide new results related to enumeration of selfavoiding random walks and calculation of the mean square endtoend distance and gyration radius of continoustime selfavoiding random walks. 
Publication Stats
90  Citations  
28.76  Total Impact Points  
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Institutions

19962008

Universidad Nacional Autónoma de México
 Department of Mathematics
Ciudad de México, Mexico City, Mexico
