In this paper, I demonstrate a density functional theory plus dynamical mean field theory study on the electronic properties of doped TiO2 rutile as well as another tetragonal phase anatase with ...oxygen vacancy. The density of states and optical properties have been obtained from the electronic structure applying screened hybrid exchange correlation density functionals. All the single-particle excitations are treated within the dynamical mean field theory for independent quasiparticles. For optical properties, excitations are considered by solving the Bethe-Salpeter equation for Coulomb correlated electron-hole duo. On this theoretical basis, band structure and optical spectra for the two structures of TiO2 are provided. Further, I compared the present results with earlier optical data of parent structure and established the increased optical efficiency in doped TiO2 with oxygen vacancy in both the structure.
•DFT + DMFT study of anatase and rutile TiO2.•Calculation of DMFT optical Properties.•Increased optical conductivity, reflectivity due to oxygen vacancy.
IrTe2 has been renewed as an interesting system showing competing phenomenon between a questionable density-wave transition near 270K followed by superconductivity with doping of high atomic number ...materials. Higher atomic numbers of Te and Ir supports strong spin-orbital coupling in this system. Using dynamical mean field theory with LDA band structure I have introduced Rashba spin orbit coupling in this system to get the interpretation for anomalous resistivity and related transition in this system. While no considerable changes are observed in DMFT results of Ir-5d band other than orbital selective pseudogap ‘pinned’ to Fermi level, Te-p band shows a van Hove singularity at the Fermi level except low temperature. Finally I discuss the implications of these results in theoretical understanding of ordering in IrTe2.
•LDA+DMFT study of IrTe2.•DMFT resitivity and optical conductivity.•DMFT calculation of ARPES and Fermi surface.
•DFT + DMFT study of Fe intercalated Bi2Se3.•Calculation of DMFT self energy, Fermi surface and susceptibility.•Orbital selectivity and Ferromagnetism.
In this paper we investigate the intercalation ...effects of Iron (Fe) in the van der Waals gap of Bi2Se3 on the magnetic and transport properties using first-principles band structure estimations combined with dynamical mean-field theory. The Dirac cone in the band structure of parent Bismuth Selenide is modified via Fe intercalation at moderate densities. Further inclusion of electronic correlations found to result in the emergence of novel and exotic properties in an intercalated Bi2Se3. Accompanied by unconventional structural effects, the onset of an orbital selective metal insulator transition in the Fe 3d orbitals brings about a magnetic phase transition in the Fe intercalated Bi2Se3. Additionally we have explored the dependency of the electron-electron correlations on the magnetic ordering and the effects of intercalation in establishing new physical properties.
I investigated the evolution of the competing orders in pressurized state of a parent and K-doped iron based spin ladder compound, BaFe2Se3, using density functional theory with the generalized ...gradient approximation. Using multi orbital dynamical mean field theory it is shown that strong, electronic correlations along with block antiferromagnetic order create a gapped Fermi surface, giving rise to an insulating state which is followed by metallic phase with appropriate pressure and doping. A good qualititative similarity with the earlier experimental transport data is observed. Suppression of antiferromagnetic ordering with pressure and K doping is explained within a strong correlation view. These results points out close analogy between antiferromagnetic insulator and superconductor state of BaFe2Se3.
This laboratory experimental study investigates the temporal evolution of the size distribution of subsurface oil droplets generated as breaking waves entrain oil slicks. The measurements are ...performed for varying wave energy, as well as large variations in oil viscosity and oil‐water interfacial tension, the latter achieved by premixing the oil with dispersant. In situ measurements using digital inline holography at two magnifications are applied for measuring the droplet sizes and Particle Image Velocimetry (PIV) for determining the temporal evolution of turbulence after wave breaking. All early (2–10 s) size distributions have two distinct size ranges with different slopes. For low dispersant to oil ratios (DOR), the transition between them could be predicted based on a turbulent Weber (We) number in the 2–4 range, suggesting that turbulence plays an important role. For smaller droplets, all the number size distributions have power of about −2.1, and for larger droplets, the power decreases well below −3. The measured steepening of the size distribution over time is predicted by a simple model involving buoyant rise and turbulence dispersion. Conversely, for DOR 1:100 and 1:25 oils, the diameter of slope transition decreases from ∼1 mm to 46 and 14 µm, respectively, much faster than the We‐based prediction, and the size distribution steepens with increasing DOR. Furthermore, the concentration of micron‐sized droplets of DOR 1:25 oil increases for the first 10 min after entrainment. These phenomena are presumably caused by the observed formation and breakup oil microthreads associated with tip streaming.
Key Points
Oil droplet size distribution generated by waves has two ranges; the transition between them is predictable by the turbulent Weber number
The size distribution steepens over time at a rate predictable by a model involving buoyant rise and turbulence dispersion
The size distribution steepens with increasing dispersant concentration due to generation and breakup of microthreads
AbstractThe current study deals with the oblique wave trapping by bottom-standing and surface-piercing porous structures of finite width placed at a finite distance from a vertical rigid wall. Using ...the Sollitt and Cross model for wave motion within the porous structure, the problems are analyzed based on the small-amplitude water wave theory in water of finite depth. The solutions of the associated boundary value problems are obtained analytically using the eigenfunction expansion method and numerically using a multidomain boundary-element method. In the boundary-element method, the boundary value problems are converted into integral equations over the physical boundaries. The physical boundaries are discretized into a finite number of elements to obtain a system of linear algebraic equations. Various aspects of structural configurations, in trapping surface gravity waves, are analyzed from the computed results on the reflection coefficients and the hydrodynamic forces. Suitable arrangements of the rigid wall and partial porous structure of specific configurations can provide long-term and cost-effective solutions for protecting various marine facilities from wave attack.
•A model using boundary element method is developed to study scattering of gravity waves by a pair of trenches.•Known results in the literature for single trench are reproduced and validated.•The ...problems are studied under small amplitude water wave theory in two-dimensions.•The study reveals the occurrence of Bragg reflection in case of a multiple trenches.•Number of sub-harmonic peaks in Bragg reflection is two less than the number of trenches.
A numerical model based on boundary element method is developed to study the scattering of surface gravity waves over a pair of trenches of varied configurations under the assumption of small amplitude water wave theory. Both the cases of symmetric and asymmetric trenches are considered in the present study. The accuracy of the numerical results is validated by comparing the reflection and transmission coefficients with energy identity, and the known results associated with single trench available in the literature. The study reveals that wave reflection decreases in an oscillatory manner with an increase in trench width. Moreover, Bragg resonance in wave reflection is observed for wave number corresponding to waves in shallow and intermediate depths in the case of a pair of trenches. Further, Bragg reflection increases with an increase in the number of trenches. In the case of multiple trenches, subharmonic peaks in Bragg reflection are depicted and the number of subharmonic peaks between two harmonic peaks is found to be two less than the number of trenches. However, for triangular trenches, the occurrence of the subharmonic peak is invariant of the number of trenches and the same vanishes for larger trench depth. Irrespective of trench configurations, wave reflection follows certain uniform oscillatory pattern with an increase in the gap between the trenches in case of deep water.
The present study deals with the oblique wave scattering by a floating flexible porous membrane under the assumptions of small amplitude water wave theory and membrane response in both the cases of ...finite and infinite water depths. Using the Green’s function technique, the boundary value problems are converted into pairs of Fredholm integral equations in terms of the velocity potentials and their normal derivatives along the membrane. Using Simpson’s quadrature formula, various integrals are evaluated and the system of integral equations are reduced to a system of linear algebraic equations which are solved to find various physical quantities of interests. Energy balance relations are derived and used to check the accuracy of the computational results. Several results of physical interests are computed and analyzed to study the effects of various wave and structural parameters. The present study will be of immense importance in creating tranquility zone for protecting coastal infrastructures through the use of floating flexible porous membrane. The concept and methodology can be used to deal with wave-structure interaction problems in related branches of mathematical physics and engineering.
•Scattering of oblique gravity waves by vertical flexible porous membranes is studied.•Analytic solution of the BVPs is obtained using eigenfunction expansion method.•Numerical solution of the BVPs ...is obtained using coupled boundary element-finite difference method.•Effectiveness of the vertical membranes as wave barriers is analyzed.
The interaction of obliquely incident surface gravity waves with a vertical flexible permeable submerged membrane wave barrier is investigated in the context of three-dimensional linear water wave theory. From the general formulation of the submerged membrane barrier, the performance of bottom-standing, surface-piercing and fully extended membrane wave barriers are analyzed for various values of wave and structural parameters. The analytic solution of the physical problem is obtained using eigenfunction expansion method and a coupled boundary element-finite difference method has been used to get the numerical solution. In the boundary element method, since the boundary condition on the membrane barrier is not known a priori, the membrane response and velocity potentials are solved simultaneously using appropriate discretization with the help of finite difference scheme. The convergence of the analytic and numerical solution techniques is discussed. The study reveals that for suitable combination of wave and structural parameters, approximately (45–50)% incident wave energy can be dissipated irrespective of membrane barrier configurations. Further, in certain situations, nearly full wave reflection and zero transmission occur for all barrier configurations. The study will be useful in the design of flexible permeable membrane to act as an effective wave barrier for creation of tranquility zone in the marine environment.
Oblique surface gravity wave scattering by a floating flexible porous plate is investigated in water of finite and infinite depths under the assumption of small amplitude water wave theory and ...structural response. Using the Greens function technique, the boundary value problems are converted into a system of Fredholm type integral equations in terms of the velocity potentials and their normal derivatives along the plates which are handled for solutions using Simpsons quadrature formula. Energy relations are derived to check the accuracy of the computed results. Various results of physical interests are computed and analyzed to study the roles of structural flexibility and porosity, wave period and angle of incidence on wave scattering by the plate. Certain results are analyzed to study the effect of edge conditions on the scattering of surface waves by the flexible porous plate. It is observed that depending on the heading angle of the incident waves, with suitable positioning of the plate, tranquility zone can be created by a flexible floating plate. Moreover, the study reveals that a major part of the wave energy can be dissipated with the introduction of structural porosity which will be of immense help in the creation of a tranquility zone for the protection of various marine facilities and infrastructures.
PDF
