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The present study pertains to magnetoelectric coupling and energy storage analysis of (1 − x)BiFe0.95Mn0.05O3-xBaTiO3 (BFMO-BT) with x = 0.1, 0.2, 0.3 lead free solid solutions. BFMO-BT solid solutions possessed a cubic structure as confirmed from powder XRD and the Rietveld refinement. A maximum ferroelectric polarization of 0.82 μC/cm2 was observed in BFMO-0.3BT. BFMO-0.3BT exhibited a maximum energy storage density (WU) of 1.97 J/cm3 and an energy conversion efficiency of 81.7%. Enhanced bulk magnetization was associated with the lattice defects; however, it decreased with increased BT content. For BFMO-0.3BT, temperature dependent susceptibility, dielectric measurement, and differential scanning calorimetry measurement revealed the magnetic transition temperature to be 275 °C, 293 °C, and 223 °C, respectively. The linear magnetoelectric coupling coefficient was measured by quantifying change in maximum polarization with respect to the applied magnetic field and was found to be 28.55 mV cm−1 Oe for BFMO-0.3BT. Conductivity measurements of BFMO-0.3BT revealed a maximum value of activation energy, i.e., 0.21 eV at 1 kHz. [ABSTRACT FROM AUTHOR]

The exact power optimization of a thermoelectric generator is performed under the simultaneous presence of internal and external irreversibilities—modeled as nonideal thermal contacts and Joule heating, respectively. We consider a modification of the constant properties model whereby thermal conductivity of the thermoelectric material has spatial dependence, giving an asymmetric fraction of the Joule heat dumped in each reservoir. In particular, with a linear form of this dependence, the heat leakage term drops out as well as Joule heat is dumped only on one side. Exact expressions for efficiency at maximum power in each of these regimes are derived and are compared at thermal impedance matching and close to equilibrium, where interesting, stepwise changes in efficiency at maximum power are observed. The present analysis leads to the inference that higher values of efficiency at maximum power are obtained when both internal and external irreversibilities are taken on the hot side. [ABSTRACT FROM AUTHOR]

We demonstrate that the atom-based charge model implemented in the current versions of the density functional tight binding (DFTB) method fails to reproduce the correct charge distribution of a range of systems, including homonuclear molecules, graphene, and nanotubes, resulting in serious distortions in the electrostatic interactions for such systems caused by the missing quadrupole moments. In particular, this failure seriously impacts the long- and medium-range interaction energies of the DFTB plus dispersion (DFTB-D) model, leading to incorrect predictions of translational or rotational barriers in such systems. We show explicitly on examples of H2 and N2 that correct quadrupole moments—and consequently correct electrostatic interactions—can be restored in such systems by adding additional bond (ghost) sites to the homonuclear molecules. Attempts to determine the point charges associated with the additional sites using the usual Mulliken population analysis lead to unphysical results. Instead, these charges can be determined using the actual DFTB densities used in the parameterization process. For homonuclear molecules, we propose an extension to the DFTB-D model by adding charges that reproduce the physically correct quadrupolar charge distribution. The resulting DFTB-D-Q model greatly improves the rotational barriers for interactions of molecular hydrogen and nitrogen with benzene. [ABSTRACT FROM AUTHOR]

Generally, the phase structure change of Pb(B' B'')O3–PZT solid solutions near a morphotropic phase boundary (MPB) can be originated from composition variations. Here our results show that the excess PbO and the sintering temperature can also result in the ferroelectric phase structure change in the Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 (PNN–PZT)-based ceramics near the MPB. The dielectric, piezoelectric, and ferroelectric properties are dependent on the tetragonal phase content (TP) which is closely associated with the excess PbO and the sintering temperature. The temperature dependence of the polarization (P)–electric field (E) hysteresis loops reveals that the tetragonal phase in the PNN–PZT-based ceramics has a lower activation energy (Ea) for domain wall movement than that of the rhombohedral phase, thus resulting in easier polarization rotation. This is responsible for the phase structure–electrical property relationships in the PNN–PZT-based ceramics, exhibiting the dependence of the tetragonal phase content (TP) on the electrical properties. [ABSTRACT FROM AUTHOR]

The transient response of a molecular junction excited by a single laser pulse or by a sequence of pulses is studied theoretically utilizing a density matrix description. The approach focuses on the sequential transmission regime and accounts for intramolecular vibrations and vibrational relaxation. Besides the optical excitation of the molecule, also the laser pulse action on the leads is considered. It is accounted for by collective plasmon excitations which also couple to the molecular transitions. Transient currents are calculated as well as averaged dc resulting from a huge sequence of laser pulses. While the transient currents give some insight into the dynamics of the junctions, the averaged dc is ready to be measured in the experiment. Different enhancement effects due to resonant lead-plasmon excitations are highlighted. [ABSTRACT FROM AUTHOR]

With the advent of improved computational resources, alternate design approaches that explicitly account for uncertainty in predictions, such as robust- and reliability-based design, are superseding deterministic design approaches in aerospace applications. In this context, accounting for the structural uncertainties in turbulence models has been identified as the greatest challenge toward simulation based design. At present, the primary methodology to estimate the structural uncertainty in turbulence models is based on tensor perturbations applied to the modeled Reynolds stress tensor. This methodology has been applied with success to a variety of problems in engineering analysis and design under uncertainty. However, the modeling rationale of this perturbation approach is still not unearthed. While we know that the procedure works in generating uncertainty estimates that account for the discrepancy in turbulence simulations, we do not know why it works or even how exactly it works. This may lead to its application to cases of turbulent flows or under conditions where it should not perform well. This could potentially lead to analyses that are misleading, or even designs that are hazardous. In this article, we outline the underlying modeling structure represented by this tensor perturbation procedure. The exact limitations addressed by each step of the perturbation methodology are isolated and explicated. This analysis enables us to identify the limitations of this procedure and outline the specific phenomena and types of turbulence model uncertainty where its application would be equivocal. Additionally, we outline how this enables us to derive quasirealizability conditions on the perturbations. [ABSTRACT FROM AUTHOR]