Anomalies in a waterlike model confined between plates

Using molecular dynamic simulations we study a waterlike model confined between two fixed hydrophobic plates. The system is tested for density, diffusion and structural anomalous behavior and compared with the bulk results. Within the range of confining distances we had explored we observe that in the pressure-temperature phase diagram the temperature of maximum density (TMD line), the temperature of maximum and minimum diffusion occur at lower temperatures when compared with the bulk values. For distances between the two layers below a certain threshold ,$d\le d_c$, only two layers of particles are formed, for $d\ge d_c$ three or more layers are formed. In the case of three layers the central layer stays liquid while the contact layers crystallize. This result is in agreement with simulations for atomistic models

Structure and anomalous solubility for hard spheres in an associating lattice gas model

In this paper we investigate the solubility of a hard-sphere gas in a solvent modeled as an associating lattice gas. The solution phase diagram for solute at 5% is compared with the phase diagram of the original solute free model. Model properties are investigated both through Monte Carlo simulations and a cluster approximation. The model solubility is computed via simulations and is shown to exhibit a minimum as a function of temperature. The line of minimum solubility (TmS) coincides with the line of maximum density (TMD) for different solvent chemical potentials, in accordance with the literature on continuous realistic models and on the "cavity" picture. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4743635]Conselho Nacional de Pesquisas (CNPq)Conselho Nacional de Pesquisas (CNPq) [475039/2010-6, 472210/2011-4]CAPESCapesInstituto Nacional de Ciencia e Tecnologia de Fluidos Complexos (INCTFCx)Instituto Nacional de Ciencia e Tecnologia de FLUIDOS COMPLEXOS (INCT-FCx)Universidade Federal de Santa CatarinaUniversidade Federal de Santa Catarin

Model of waterlike fluid under confinement for hydrophobic and hydrophilic particle-plate interaction potentials

Molecular dynamic simulations were employed to study a waterlike model confined between hydrophobic and hydrophilic plates. The phase behavior of this system is obtained for different distances between the plates and particle-plate potentials. For both hydrophobic and hydrophilic walls, there are the formation of layers. Crystallization occurs at lower temperature at the contact layer than at the middle layer. In addition, the melting temperature decreases as the plates become more hydrophobic. Similarly, the temperatures of maximum density and extremum diffusivity decrease with hydrophobicity

Relation between occupation in the first coordination shells and widom line in core-softened potentials

Three core-softened families of potentials are checked for the presence of density and diffusion anomalies. These potentials exhibit a repulsive core with a softening region and at larger distances an attractive well. We found that the region in the pressure-temperature phase diagram in which the anomalies are present increases if the slope between the core-softened scale and the attractive part of the potential decreases. The anomalous region also increases if the range of the core-softened or of the attractive part of the potential decreases. We also show that the presence of the density anomaly is consistent with the non-monotonic changes of the radial distribution function at each one of the two scales when temperature and density are varied. Then, using this anomalous behavior of the structure we show that the pressure and the temperature at which the radial distribution function of one of the two length scales equals the radial distribution function of the other length scales identify the Widom line

A Case of Pulmonary Cement Embolism Managed through Symptomatic Treatment

Objective. This case describes symptomatic pulmonary cement embolism as a rare postvertebroplasty complication and highlights its critical yet ill-defined management. Background. Pulmonary cement embolism (PCE) is a feared complication of vertebroplasty in the treatment of vertebral fractures. While the majority of PCEs are asymptomatic, symptomatic PCEs often present with chest pain, tachycardia, signs of severe respiratory distress, and death. Computer tomography angiogram (CTA) allows visualization of cement within the pulmonary vasculature. Despite the well-established risk of PCE, clinical management is unclear with limited research on treatment options. Reported treatments include anticoagulation, embolectomy, CPR, and supportive care and observation. Report. We report the case of a 75-year-old woman who experienced shortness of breath, tachypnea, tachycardia, hypertension, and hypoxemia five days following a corrective surgery for a compression fracture of L3 with pedicle screw fixation, fusion of L2 through L4, and L2 vertebral body cement augmentation with polymethyl methacrylate. Results. Breath sounds were diminished bilaterally with respiratory alkalosis and hypoxemia evident on arterial blood gas. CTA revealed intravasated cement throughout the right lung, including the pulmonary artery and upper and middle lobar arteries. The proposed mechanism is embolization of cement particles from the lumbar veins, which also showed intravasation. Due to the inorganic nature of the occluding material, the use of a thrombolytic agent was ruled against. Treatment included bronchodilators, 3 L of oxygen via nasal cannula, and prophylactic antibiotics, pulmonary toilet, and incentive spirometry. Symptomatic management was continued until she was discharged from the hospital in a stable condition. Conclusions. Postvertebroplasty pulmonary cement embolisms can be managed conservatively, without the use of anticoagulant or thrombolytic agents. This case illustrates a variation of care for this rare presentation and adds to the sparse literature on the management of PCEs

Thermodynamic, dynamic, structural, and excess entropy anomalies for core-softened potentials

Using molecular dynamic simulations we study three families of continuous core-softened potentials consisting of two length scales: a shoulder scale and an attractive scale. All the families have the same slope between the two length scales but exhibit different potential energy gap between them. For each family three shoulder depths are analyzed. We show that all these systems exhibit a liquid-liquid phase transition between a high density liquid phase and a low density liquid phase ending at a critical point. The critical temperature is the same for all cases suggesting that the critical temperature is only dependent on the slope between the two scales. The critical pressure decreases with the decrease of the potential energy gap between the two scales suggesting that the pressure is responsible for forming the high density liquid. We also show, using the radial distribution function and the excess entropy analysis, that the density, the diffusion and the structural anomalies are present if particles move from the attractive scale to the shoulder scale with the increase of the temperature indicating that the anomalous behavior depends only in what happens up to the second coordination shell