Nonquiescent relaxation in entangled polymer liquids after step shear

Large step shear experiments revealed through particle tracking velocimetry that entangled polymeric liquids display either internal macroscopic movements upon shear cessation or rupturelike behavior during shear. Visible inhomogeneous motions were detected in five samples with the number of entanglements per chain ranging from 20 to 130 at amplitudes of step strain as low as 135%.     

Towerlike SBA-15: base and (10)-specific coalescence of a silicate-encased hexagonal mesophase tailored by nonionic triblock copolymers

Hydrothermal templating of mesoporous molecular sieves by nonionic triblock copolymers [poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) (PEO-PPO-PEO)] at specific block lengths of EO(20)PO(70)EO(20) and selected 2 M HCl dosage (pH -0.3) caused the formation of micrometer-sized SBA-15 hexagons with well-ordered hexagonal pore channels (pore size and wall thickness of approximately 6 nm and pore-to-pore distance of approximately 12 nm) after template removal. For a beneficial lower surface energy, these {10} laterally coalesced hexagons tend to stack imperfectly over the base into towerlike entities, leaving dislocations and faults within the single domain thus formed. Evidence for the mechanism of Brownian motion/coalescence of the hexagonal-mesophase particulates, previously suggested for MCM-41 accretion in the presence of cationic surfactant, is more clearly identifiable in the present low-pH case of amphiphilic block copolymer templates and linear silica oligomers.     

Condensation and relaxation/transformation of dense t-ZrO2 nanoparticles

Dense tetragonal (t)-ZrO(2) nanocondensates were synthesized under very rapid heating and cooling by pulsed Nd-YAG (YAG--yttrium aluminum garnet) laser ablation with oxygen background gas and characterized by electron diffraction. The t-ZrO(2) nanoparticles with a residual stress up to about 5 GPa tended to form deformation twins/faults upon local electron dosage. By contrast, the t-ZrO(2) nanoparticles formed at an-order-of-magnitude higher power have a residual stress above 6 GPa and tended to transform into a metastable cubic (c) phase vulnerable to amorphization. The relaxation/transformation of the self-constrained t-ZrO(2) nanoparticles can be rationalized by a lowering of internal energy under the influence of resolved shear stress and local electron heating.     

Thermal Charging Optimization of a Wavy-Shaped Nano-Enhanced Thermal Storage Unit

A wavy shape was used to enhance the thermal heat transfer in a shell-tube latent heat thermal energy storage (LHTES) unit. The thermal storage unit was filled with CuO–coconut oil nano-enhanced phase change material (NePCM). The enthalpy-porosity approach was employed to model the phase change heat transfer in the presence of natural convection effects in the molten NePCM. The finite element method was applied to integrate the governing equations for fluid motion and phase change heat transfer. The impact of wave amplitude and wave number of the heated tube, as well as the volume concertation of nanoparticles on the full-charging time of the LHTES unit, was addressed. The Taguchi optimization method was used to find an optimum design of the LHTES unit. The results showed that an increase in the volume fraction of nanoparticles reduces the charging time. Moreover, the waviness of the tube resists the natural convection flow circulation in the phase change domain and could increase the charging time.     

Identification of tire forces using Dual Unscented Kalman Filter algorithm

Nowadays, application of active control systems in vehicles has been developed in order to increase safety and steerability. In these systems, using an appropriate dynamic model can be very effective in increasing the accuracy of simulations and analysis. Tire-road forces are crucial in vehicle dynamics and control since they are the only forces that a vehicle experiences from the ground and have maximum uncertainty on vehicle dynamic model. In order to simulate the non-linear regimes of vehicle motion, the ‘Pacejka’ tire model is being utilized. In this paper, a dynamic model with Dual Unscented Kalman Filter algorithm has been utilized to identify the lateral forces, side slip angle, and normal forces of tires. In order to solve the non-linear least squares problem, these parameters were given as input to the hybrid Levenberg–Marquardt and quasi Newton algorithm to find the Pacejka tire model coefficients in the offline mode. Four degrees of freedom vehicle model combined with Pacejka tire model are used for simulation in various maneuvers. Results show appropriate compatibility with CarSim software.     

Numerical simulation of cavitation around a two-dimensional hydrofoil using VOF method and LES turbulence model

In this paper simulation of cavitating flow over the Clark-Y hydrofoil is reported using the large eddy simulation (LES) turbulence model and volume of fluid (VOF) technique. We applied an incompressible LES modelling approach based on an implicit method for the subgrid terms. To apply the cavitation model, the flow has been considered as a single fluid, two-phase mixture. A transport equation model for the local volume fraction of vapour is solved and a finite rate mass transfer model is used for the vapourization and condensation processes. A compressive volume of fluid (VOF) method is applied to track the interface of liquid and vapour phases. This simulation is performed using a finite volume, two phase solver available in the framework of the OpenFOAM (Open Field Operation and Manipulation) software package. Simulation is performed for the cloud and super-cavitation regimes, i.e., σ = 0.8, 0.4, 0.28. We compared the results of two different mass transfer models, namely Kunz and Sauer models. The results of our simulation are compared for cavitation dynamics, starting point of cavitation, cavity’s diameter and force coefficients with the experimental data, where available. For both of steady state and transient conditions, suitable accuracy has been observed for cavitation dynamics and force coefficients.     

In-plane transport and enhanced thermoelectric performance in thin films of the topological insulators Bi₂Te₃ and Bi₂Se₃

Several small-band-gap semiconductors are now known to protect metallic surface states as a consequence of the topology of the bulk electron wave functions. The known "topological insulators" with this behavior include the important thermoelectric materials Bi?Te? and Bi?Se?, whose surfaces are observed in photoemission experiments to have an unusual electronic structure with a single Dirac cone. We study in-plane (i.e., horizontal) transport in thin films made of these materials. The surface states from top and bottom surfaces hybridize, and conventional diffusive transport predicts that the tunable hybridization-induced band gap leads to increased thermoelectric performance at low temperatures. Beyond simple diffusive transport, the conductivity shows a crossover from the spin-orbit-induced antilocalization at a single surface to ordinary localization.     

Density functional theory calculations of dense TiO2 polymorphs: implication for visible-light-responsive photocatalysts

Structural parameters and electronic band gaps of dense TiO(2) polymorphs, i.e., alpha-PbO(2), baddeleyite, fluorite, and cotunnite types of structures, were calculated using a first-principles density functional method with local-density approximation. The ambient phases, i.e., rutile and anatase, with known theoretical and experimental data were used to ensure the validity of the calculations. The fluorite-type TiO(2) turned out to have the narrowest band gap, 1.08 or 2.18 eV after applying a very approximate band gap correction, due to highly symmetrical TiO(8) polyhedra with Ti(3d) and O(2p) orbitals in the most mixed state. Ti with eight coordinated oxygens, as feasible under high pressure or residual stress, may have potential applications as a visible-light-responsive photocatalyst.     

Syzygy and Torsionless Modules with Respect to a Semidualizing Module

This paper aims at generalizing the notions of “Auslander dual”, “k-torsionless” and “k-th syzygy” modules to the relative setting with respect to a semidualizing module. It is shown that the “relative” Auslander dual shares many nice properties with the Auslander dual originally introduced by Auslander and Bridger. It is also shown the interplay between the “relative” version of “k-torsionless” and “k-th syzygy” modules parallels that of k-torsionless and k-th syzygy modules.