On Calculation of Thermal Conductivity from Einstein Relation in Equilibrium MD

In equilibrium molecular dynamics, Einstein relation can be used to calculate the thermal conductivity. This method is equivalent to Green-Kubo relation and it does not require a derivation of an analytical form for the heat current. However, it is not commonly used as Green-Kubo relationship. Its wide use is hindered by the lack of a proper definition for integrated heat current (energy moment) under periodic boundary conditions. In this paper, we developed an appropriate definition for integrated heat current to calculate thermal conductivity of solids under periodic conditions. We applied this method to solid argon and silicon based systems; compared and contrasted with the Green-Kubo approach.Comment: We updated this manuscript from second version by changing the title and abstract. This paper is submitted to J. Chem. Phy

Acetonitrile confined in carbon nanotubes, part I: Structure, dynamic and transport properties

In the first part of our study, here an all atom molecular dynamic study on the effect of confinement on structure, dynamic and transport properties of acetonitrile is presented. For this purpose, Single Walled Carbon Nanotubes (SWCNTs) were filled with the acetonitrile by employing isothermal-isobaric ensemble followed by canonical ensemble molecular dynamics simulations for investigating interactions between the acetonitrile and SWCNTs. Several interesting features of the acetonitrile were identified as the diameter of CNTs becomes smaller. First, two distinct regions were identified i.e., a core region along the longitudinal direction dominated by rarefaction effects and an interface shell with relatively high density of fluid. Volume of rarefied region decreases with larger values of tube diameters. Secondly, interfacial mobility in the vicinity fluid-CNT interface favors axial mean squared displacements of the acetonitrile molecules. Analyses also show that radial mobility of the molecules strongly depends on the size of the core region and diameter of the tube whereas the axial self-diffusion coefficient varies almost exponentially with the tube diameter. Thirdly, a preferred coordination between each pair of the C (methyl group carbon), C (nitrile group carbon) and N atoms, and an ordering in the vicinity of wall were observed contrary to those of larger tubes. Fourthly, we observed that the E2g mode frequencies of SWCNT dominates those of C1-C2-N bending and C1-C2 stretching modes. The frequencies of both SWCNTs and those of the fluid are the same in these modes. Lastly, the shear viscosity diminishes with the diameter of the tube. © 2020 Elsevier B.V

Dielectric properties of acetonitrile confined in carbon nanotubes

This study addresses numerical investigation of dielectric properties of acetonitrile confined in Single Walled Carbon Nano Tubes (SWCNTs). Frequency dependent permittivity have been computed by assuming whether interactions among the Acetonitrile (ACN) molecules exist or not. Both axial and radial dielectric permittivity show tube diameter dependence. Static dielectric permittivity becomes larger with the diameter of the tubes but still smaller than that of the bulk state as well. Furthermore, an anomalous decrease in radial component of dielectric permittivity was observed. Bending modes and stretching modes between the Carbon atoms affect the variation of dielectric permittivities as well. Moreover, Kirkwood correlation factor, g factor, firmly influenced by the size of the tube and Knudsen region where immediate interactions of ACN molecules start to develop in the this region for narrower tubes too. Both relaxation and reorientation of Acetonitrile inside the CNTs are slower than those of the bulk state. © 2019 Elsevier B.V

EFFECT OF ALLOYING ELEMENTS ON THE FORMATION OF FeTiH4: AN AB INITIO STUDY

FeTi can store 3.7 wt% hydrogen if it is synthesized in the form of FeTiH4. In the present study, candidate alloying elements were investigated that would decrease the formation energy of this hydride, using first principles calculations within the generalized gradient approximation (GGA) to density functional theory (DFT). Selected alloying elements are Co, Mg, Mo, Ni, Nb, V and Zr, and they were substituted for Fe or Ti atoms separately. Their effects on the formation energy of FeTiH4 were analyzed on the basis of electronic structure. It was found that Zr, Nb, Mo and Mg substitution for Fe decreases the formation energy of the hydride considerably. Stabilization is achieved by forming stronger bonds between hydrogen atoms and rest of the Fe atoms in the structure which is facilitated by the antibonding between the hydrogen atoms and the substituted high tendency hydride forming element

On self-propulsion assessment of marine vehicles

Estimation of ship self-propulsion is important for the selection of the propulsion system and the main engine so that the ship can move forward with the required speed. Resistance characteristics of the vessel or the open-water performance of a propeller only are not usually enough to assess the working conditions of the ship. Both in numerical simulations and in experiments; there is a need to treat the propulsion system and the hull as a whole for a better estimation of the self-propulsion parameters. In this study, the self-propulsion points of one submarine (DARPA Suboff) and two surface piercing vessels (KCS and DTC) were obtained with methods based on computational fluid dynamics (CFD) approach. The self-propulsion points were also calculated by a classical engineering approach that makes use of the empirical relations that may be found in the literature. The results were evaluated with respect to the experiments and numerical results generated by other researchers in this field. It was found that the self-propulsion points of traditional ship forms can be very closely approximated with a classical engineering approach, given the basic geometric and the hydrostatic properties of the hull and the propeller. © 2018, Brodarski Institute. All rights reserved

A Comparison of Surgical Treatments for Superior Semicircular Canal Dehiscence: A Systematic Review

OBJECTIVE: We investigate the postoperative subjective and objective outcomes of different surgical treatments for superior semicircular canal dehiscence (SSCD): vestibular signs, auditory signs, vestibular evoked myogenic potential test, pure tone audiogram, speech audiogram, or video-nystagmography. DATA SOURCES: An electronic search performed in the PubMed, Cochrane Library, and EMBASE databases on 15th of September 2015. A systematic search was conducted. Articles were included if written in English, Dutch, German, or French language. STUDY SELECTION: Original studies reporting on the pre and postoperative subjective and/or objective outcomes of surgical treatments for superior semicircular canal dehiscence were included. DATA EXTRACTION: The methodological quality of the studies was independently assessed by two reviewers using a constructed critical appraisal, to assess the directness of evidence and the risk of bias. The results of the pre and postoperative subjective and/or objective outcomes were extracted. DATA SYNTHESIS: Comparative study was conducted. CONCLUSION: Surgical treatment for SSCD is particularly effective for vestibular symptoms and there is no evidence for improvement of hearing loss after surgical treatment. Since plugging using transmastoid approach had a lower complication rate, lower revision rate, and a shorter hospital stay, this treatment is recommended in high disabled SSCD patients

Tailoring thermal conductivity of silicon/germanium nanowires utilizing core-shell architecture

Low-dimensional nanostructured materials show large variations in their thermal transport properties. In this work, we investigate the influence of the core-shell architecture on nanowire (1D) thermal conductivity and evaluate its validity as a strategy to achieve a better thermoelectric performance. To obtain the thermal conductivity values, equilibrium molecular dynamics simulations are conducted for core-shell nanowires of silicon and germanium. To explore the parameter space, we have calculated thermal conductivity values of the Si-core/Ge-shell and Ge-core/Si-shell nanowires having different cross-sectional sizes and core contents at several temperatures. Our results indicate that (1) increasing the cross-sectional area of pristine Si and pristine Ge nanowires increases the thermal conductivity, (2) increasing the Ge core size in the Ge-core/Si-shell structure results in a decrease in the thermal conductivity at 300 K, (3) the thermal conductivity of the Sicore/Ge-shell nanowires demonstrates a minima at a specific core size, (4) no significant variation in the thermal conductivity is observed in nanowires for temperatures larger than 300 K, and (5) the predicted thermal conductivity within the frame of applied geometrical constraints is found to be around 10 W/(mK) for the Si and Ge core-shell architecture with a smooth interface. The value is still higher than the amorphous limit (1 W/(mK)). This represents a significant reduction in thermal conductivity with respect to their bulk crystalline and pristine nanowire forms. Furthermore, we observed additional suppression of thermal conductivity through the introduction of interface roughness to Si/Ge core-shell nanowires. Published by AIP Publishing