Search results for "dynamics."
showing 10 items of 9637 documents
Two prospective Li-based half-Heusler alloys for spintronic applications based on structural stability and spin–orbit effect
2017
To search for half-metallic materials for spintronic applications, instead of using an expensive trial-and-error experimental scheme, it is more efficient to use first-principles calculations to design materials first, and then grow them. In particular, using a priori information of the structural stability and the effect of the spin–orbit interaction (SOI) enables experimentalists to focus on favorable properties that make growing half-metals easier. We suggest that using acoustic phonon spectra is the best way to address the stability of promising half-metallic materials. Additionally, by carrying out accurate first-principles calculations, we propose two criteria for neglecting the SOI s…
Long term stability testing of oxide unicouple thermoelectric modules
2019
Thermoelectric devices based on oxides are good candidates for energy harvesting technologies for use in aggressive conditions where the materials should withstand high temperatures and corrosive environments over prolonged time. This leads to a natural concern for the stability of the electrical contacts, especially on the hot side of the module. In this work, we have assembled several prototype unicouple thermoelectric modules made by pyrolyzed and spark plasma sintered n-type CaMnO3 and p-type Ca3Co4O9 and then tested under different conditions mimicking end-user applications. For baseline experiments we have chosen to use nickel as the contact material in order to show the effect of its…
Simulation of IQE tuning of individual cells for DC-balancing multijunction tandem cells
2016
In the present work, the performance of stacks of cells connected in series is examined at different levels of internal quantum efficiency (IQE). Incident photons, generated by employing the ASTM G173-03 data set, are accounted for individually as they interact with the stack of cells. The efficiencies of the devices studied are dependent upon the DC balance throughout the stack of cells. It is demonstrated that reducing the internal quantum efficiency of upper cells can lead to a better DC balance and thereby higher efficiency.
Optical study for springback prediction, thickness reduction and forces variations on single point incremental forming
2019
Abstract The goal of the present work is to present an experimental study regarding the influence of the main technological influence factors such as the vertical step and the punch diameter on the single point incremental forming process (SPIF). In this paper we estimate the influence of these two factors on springback, thickness reduction and forces. Both parameters were varied on two levels: (d) punch diameter 6 and 10 mm and (s) vertical step 0,1 and 0,5 mm. The experiments were done on experimental layout composed by a robot, a clamping system that contains the die’s lower part and the optical system.
Quantification of relaxor behavior in (1 − x)Na0.5Bi0.5TiO3 – xCaTiO3 lead-free ceramics system
2019
Abstract This work examines the relaxor behavior of lead-free ceramic (1 − x)Na0.5Bi0.5TiO3–xCaTiO3 systems. A stable rhombohedral (R3c) phase is detected at room temperature for all compositions by XRD and Raman spectroscopy. Relaxor behavior was observed in the temperature range 300 K - 400 K for all materials. Ceramics exhibit normal ferroelectric properties at room temperature, and then they develop relaxor characteristics with increasing temperature showing the same dispersive properties. This work quantifies the relaxor phenomenon at low temperature. For instance, the maximum temperature of relaxor and the order of dispersion were determined at the strongest dispersion. Finally, the s…
Simulations of the effect of the contact energy levels on a simple model of a hot carrier cell
2016
In the present work, the performance of a simplified model of a hot carrier cell is examined at different energy levels of carrier collection. Incident photons, Monte Carlo generated by employing the ASTM G173-03 data set, are accounted for individually as they interact with the cell. It is assumed that the carriers can be collected ultra-fast, thus avoiding considering hot carrier thermalisation effects. Although the model is preliminary and lacking some mechanisms of hot carrier cells, it has been demonstrated that the present approach to modelling hot carrier solar cells can be developed into fully working models. Some effects of the absorption energy levels in the valence band have been…
On the ‘expanded local mode’ approach applied to the methane molecule: isotopic substitution CH2D2←CH4
2011
On the basis of a compilation of the ‘expanded local mode’ model and the general isotopic substitution theory, sets of simple analytical relations between different spectroscopic parameters (harmonic frequencies, ωλ, anharmonic coefficients, x λμ, ro-vibrational coefficients, , different kinds of Fermi- and Coriolis-type interaction parameters) of the CH2D2 molecule are derived. All of them are expressed as simple functions of a few initial spectroscopic parameters of the mother, CH4, molecule. Test calculations with the derived isotopic relations show that, in spite of a total absence of initial information about the CH2D2 species, the numerical results of the calculations have a very good…
Towards highly accurate ab initio thermochemistry of larger systems: benzene.
2011
The high accuracy extrapolated ab initio thermochemistry (HEAT) protocol is applied to compute the total atomization energy (TAE) and the heat of formation of benzene. Large-scale coupled-cluster calculations with more than 1500 basis functions and 42 correlated electrons as well as zero-point energies based on full cubic and (semi)diagonal quartic force fields obtained with the coupled-cluster singles and doubles with perturbative treatment of the triples method and atomic natural orbital (ANO) triple- and quadruple-zeta basis sets are presented. The performance of modifications to the HEAT scheme and the scaling properties of its contributions with respect to the system size are investiga…
Origin of Enzymatic Kinetic Isotope Effects in Human Purine Nucleoside Phosphorylase
2017
Here we report a study of the effect of heavy isotope labeling on the reaction catalyzed by human purine nucleoside phosphorylase (hPNP) to elucidate the origin of its catalytic effect and of the enzymatic kinetic isotope effect (EKIE). Using quantum mechanical and molecular mechanical (QM/MM) molecular dynamics (MD) simulations, we study the mechanism of the hPNP enzyme and the dynamic effects by means of the calculation of the recrossing transmission coefficient. A free energy surface (FES), as a function of both a chemical and an environmental coordinate, is obtained to show the role of the environment on the chemical reaction. Analysis of reactive and nonreactive trajectories allows us …
A quantum dynamics study of the benzopyran ring opening guided by laser pulses
2014
Abstract The ring-opening photoisomerization of benzopyran, which occurs via a photochemical route involving a conical intersection, has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method (MCTDH). We introduce a mechanistic strategy to control the conversion of benzopyran to merocyanine with laser pulses. We use a six-dimensional model developed in a previous work for the potential energy surfaces (PES) based on an extension of the vibronic-coupling Hamiltonian model (diabatization method by ansatz), which depends on the most active degrees of freedom. The main objective of these quantum dynamics simulations is to provide a set of str…