Bridging the gap between atomistic and continuum models to predict dielectric and thermodynamic properties of confined fluids

Nanoconfined fluids are ubiquitous and play a prominent role in nature and technological applications. Understanding the physics of the confined fluids and obtaining atomic-level insights into their unusual properties is essential to develop and design novel nanofluidic applications related to energy, water, and health. For systems involving multiple length and time scales, atomistic simulations become forbiddingly expensive. On the other hand, classical continuum theories fails to accurately describe the fluid properties at atomic level. Thus, there is a need for a multiscale frame work to maintain the balance between accuracy and rigor of atomistic simulations and efficiency of continuum frameworks. In this work, we present an empirical potential-based quasi-continuum theory (EQT) that provides a framework to seamlessly integrate atomistic details into a continuum-based models. The main idea in EQT is to bridge the gap between atomistic and continuum models by incorporating molecular correlations, interatomic interactions, and anisotropic effects at a continuum level. We show that EQT can be used in classical density functional theory to predict the thermodynamic properties for confined fluids. Moreover, we present a hierarchical coarse-grain (CG) approach in which we coarse grain the degrees of freedom of polar liquids from the detailed all-atom (AA) level to the cheaper particle-based CG level, and to the continuum-based level. Our goal is to devise CG interaction potentials for polar liquids that reproduces not only the structure but also accurately describe the dielectric permittivity and its anisotropic nature in the confinement. Using the CG potentials in EQT we show that neglecting the tensorial form of the dielectric permittivity in the Poisson equation leads to incorrect screening and orientational polarization profiles near interfaces. Thus, using extensive molecular dynamics simulations, statistical-mechanical theories and multiscale methods, we study the out-of-plane (z-axis) and in-plane (x-y) dielectric response of protic and aprotic fluids confined inside slit-like graphene channels. We find a universal reduction in perpendicular permittivity for all the fluids. Whereas, the parallel dielectric response of polar liquids is enhanced and is proportional to dipolar correlations and density oscillation next to the interface. The perpendicular reduction and in-plane enhancement of the dielectric permittivity is attributed to the favorable in-plane (x-y plane) dipole-dipole electrostatic interactions of the interfacial fluid layer. These findings have important consequences in, developing accurate coarse-grained force fields and improving the solvent-implicit approaches often used in biology and continuum theories such as the Poisson- Boltzmann (PB) equation for accurate prediction of capacitance in the electric double-layer capacitors

A multiscale theory to determine thermodynamic properties of confined fluids

Empirical potential-based quasi-continuum theory (EQT) provides a route to incorporate atomistic detail into a continuum framework such as the Nernst- Planck equation. EQT is a simple and fast approach to predict inhomogeneous density and potential profiles of confined fluids. EQT potentials can be used to construct a grand potential functional for classical density functional theory (cDFT). The combination of EQT and cDFT provides a robust and accurate approach to predict the structure and thermodynamic properties of confined fluids at multiple length-scales, ranging from few Angstroms to macro meters. In this work, first, we demonstrate the EQT-cDFT approach by simulating sin- gle component Lennard-Jones (LJ) fluids, namely, methane and argon, confined inside slit-like channels of graphene. For these systems, we show that the EQT- cDFT can accurately predict the structure and thermodynamic properties, such as density profiles, adsorption, local pressure tensor, surface tension, and solva- tion force of confined fluids as compared to the MD simulation results. Next, we extend the EQT-cDFT approach to confined fluid mixtures and demonstrate it by simulating a mixture of methane and hydrogen inside slit-like channels of graphene. We show that the EQT-cDFT predictions for the structure of the confined fluid mixture compare well with the MD simulations results. In addi- tion, our results show that graphene slit nanopores exhibit a selective adsorption of methane over hydrogen

Verification of Legal Entities' Overpaid Claims in Value Added Tax System in Iran

This paper aims to investigate the relationship between the legal entities' overpaid claims and Value Added Tax Organization reports. The statistical population consists of those legal entities subject to the first and second phases of value added tax system operating in the city of Mashhad which have submitted their tax returns to the Tax Organization’s offices during 2008 to 2012 and claimed that their paid taxes and duties are more than those received during the relevant period. Thus, they have requested refund for overpaid taxes and duties. The results showed that there is a significant difference between their claims and reports in the Tax Organization

Evaluation of temperature rise with different curing methods and units in two composite resins

Background and Aim: The majority of commercial curing units in dentistry are of halogen lamp type. The new polymerizing units such as blue LED are introduced in recent years. One of the important side effects of light curing is the temperature rise in composite resin polymerization which can affect the vitality of tooth pulp. The purpose of this study was to evaluate the temperature rise in two different composite resins during polymerization with halogen lamps and blue LED. Materials and Methods: This experimental study investigated the temperature rise in two different composites (Hybrid, Tetric Ceram/Nanofilled, Filteke Supreme) of A2 shade polymerized with two halogen lamps (Coltolux 50, 350 mW/cm2 and Optilux 501 in standard, 820 mW/cm2 and Ramp, 100-1030 mW/cm2 operating modes) and one blue LED with the intensity of 620 mW/cm2. Five samples for each group were prepared and temperature rise was monitored using a k-type thermocouple. Data were analyzed by one-way ANOVA, two-way ANOVA and Tukey HSD tests with P<0.05 as the limit of significance. Results: Light curing units and composite resins had statistically significant influence on the temperature rise (p<0.05). Significantly, lower temperature rise occurred in case of illumination with Coltolux 50.There was no significant difference between Optilux 501 in standard curing mode and LED. Tetric Ceram showed higher temperature rise. Conclusion: According to the results of this study the high power halogen lamp and LED could produce significant heat which may be harmful to the dental pulp

The effect of curing units and methods on degree of conversion of two types of composite resins

Background and Aim: Halogen lamp is the commonly used light source for composite photo polymerization. Recently, high power halogen lamps, LED and plasma arc are introduced for improving the polymerization. The aim of this study was to investigate the effect of conventional and high power halogen lamps and LED light curing unit on degree of conversion of two different composite resins.Materials and Methods: In this in vitro experimental study two halogen units (Coltolux 50 with the intensity of  330 mW/cm2 and Optilux 501 with two different operating modes of standard with the intensity of 820 mW/cm2 and Ramp with the intentsiy of 100-1030mW/cm2) and one LED light curing unit (620 mW/cm2) were used. The composites were hybrid (Tetric ceram) and nanofilled (Filteke supreme). Each materials/curing method contained three samples and degree of conversion (DC) was measured with FTIR. Data were analyzed statistically with one way and two way ANOVA, Tukey HSD. P<0.05 was considered as the limit of significance.Results: Tetric ceram revealed higher DCthan Supreme. Tetric ceram showed a significant decrease in DC when Coltolux 50 was used in comparison to LED and Optilux 501. The latters did not show significant effect on DC of this material. DC of Supreme polymerized with various curing modes was not significantly different.Conclusion: Based on the results of this study, degree of conversion in hybrid composites was higher than nanofilled. In comparison with conventional halogen lamp (Coltolux 50), high intensity halogen lamps and LED unit significantly lead to higher degree of conversion in hybrid composites

In Vitro Microleakage of Class V Composite Restorations in Use of Three Adhesive Systems

Background and Aim: Microleakage is a drawback of composite restorations and it is more noticeable in dentinal walls. Despite advances in dentin bonding agents, no adhesive can completely eliminate microleakage and provide a hermetic seal. This study aimed to compare microleakage of three resin bonding agents namely a universal adhesive, two-step self-etch system and two-step total-etch system. Materials and Methods: This in vitro, experimental study was conducted on 68 human molars. Class V cavities were prepared in the buccal or lingual surfaces of the teeth with occlusal margins in the enamel and gingival margins in dentin. The teeth were then randomly divided into four groups of 17. Group A: Adper Single Bond 2, group B: Clearfil SE Bond, group C: Scotchbond Universal adhesive (self-etch) and group D: Scotchbond Universal adhesive (total-etch). The teeth were then restored using different bonding agents and a microhybrid composite resin. The specimens were then subjected to 1000 thermal cycles between 5-55°C. The entire restoration surface except for 1mm around the margins was coated with nail varnish. The teeth were immersed in 2% methylene blue for 24 hours and sectioned longitudinally in a buccolingual direction and observed under a stereomicroscope to determine microleakage. Microleakage in use of the three bonding agents was compared using the Kruskal Wallis test (P<0.05). Results: Based on the Kruskal Wallis test, no significant difference was noted in enamel and dentin margins among different adhesives but the enamel margin showed less microleakage than the dentin margin. Conclusion: Different adhesive systems tested in this study showed similar microleakage at the enamel and dentinal margins

Legislative Documents

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