Advanced control strategy for AC microgrids: a hybrid ANN-based adaptive PI controller with droop control and virtual impedance technique.

In this paper, an improved voltage control strategy for microgrids (MG) is proposed, using an artificial neural network (ANN)-based adaptive proportional-integral (PI) controller combined with droop control and virtual impedance techniques (VIT). The control strategy is developed to improve voltage control, power sharing and total harmonic distortion (THD) reduction in the MG systems with renewable and distributed generation (DG) sources. The VIT is used to decouple active and reactive power, reduce negative power interactions between DG's and improve the robustness of the system under varying load and generation conditions.

Direct bandgap quantum wells in hexagonal Silicon Germanium.

Silicon is indisputably the most advanced material for scalable electronics, but it is a poor choice as a light source for photonic applications, due to its indirect band gap. The recently developed hexagonal SiGe semiconductor features a direct bandgap at least for x > 0.65, and the realization of quantum heterostructures would unlock new opportunities for advanced optoelectronic devices based on the SiGe system.

Pseudo-multicomponent 1,3-dipolar cycloaddition involving metal-free generation of unactivated azomethine ylides.

The pseudo-multicomponent reaction between propargyl amine, an aldehyde and an electron-deficient alkene is described. The C-H activation takes place thermally and allows the obtaining of cycloadducts in very good yields with high diastereoselectivities. The relative configuration is determined by X-ray diffraction analysis of the chiral molecule, obtained as a single diastereoisomer, using a chiral maleimide.

Synthesis of Non-natural Aza-Iridoids Ynamides and Molecular Networking-Based Tracing of Their Bioconversion.

A synthesis of new-to-nature aza-iridoids ynamides is presented. ZrCl proved to be the best acid to perform this transformation. Various ynamides were accommodated, and -iridoids could be obtained as well.

Design Aspects of Doped CeO for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach.

CO elimination through oxidation over highly active and cost-effective catalysts is a way forward for many processes of industrial and environmental importance. In this study, doped CeO with transition metals (TM = Cu, Co, Mn, Fe, Ni, Zr, and Zn) at a level of 20 at. % was tested for CO oxidation.

A DFT study of the adsorption energy and electronic interactions of the SO molecule on a CoP hydrotreating catalyst.

The adsorption energy and electronic properties of sulfur dioxide (SO) adsorbed on different low-Miller index cobalt phosphide (CoP) surfaces were examined using density functional theory (DFT). Different surface atomic terminations and initial molecular orientations were systematically investigated in detail to determine the most active and stable surface for use as a hydrotreating catalyst. It was found that the surface catalytic reactivity of CoP and its performance were highly sensitive to the crystal plane, where the surface orientation/termination had a remarkable impact on the interfacial chemical bonding and electronic states toward the adsorption of the SO molecule.

Indirect chiral magnetic exchange through Dzyaloshinskii-Moriya-enhanced RKKY interactions in manganese oxide chains on Ir(100).

Localized electron spins can couple magnetically via the Ruderman-Kittel-Kasuya-Yosida interaction even if their wave functions lack direct overlap. Theory predicts that spin-orbit scattering leads to a Dzyaloshinskii-Moriya type enhancement of this indirect exchange interaction, giving rise to chiral exchange terms. Here we present a combined spin-polarized scanning tunneling microscopy, angle-resolved photoemission, and density functional theory study of MnO chains on Ir(100).

Efficient Green Emission from Wurtzite Al InP Nanowires.

Direct band gap III-V semiconductors, emitting efficiently in the amber-green region of the visible spectrum, are still missing, causing loss in efficiency in light emitting diodes operating in this region, a phenomenon known as the "green gap". Novel geometries and crystal symmetries however show strong promise in overcoming this limit. Here we develop a novel material system, consisting of wurtzite Al InP nanowires, which is predicted to have a direct band gap in the green region.

Correlation of the Dzyaloshinskii-Moriya interaction with Heisenberg exchange and orbital asphericity.

Chiral spin textures of a ferromagnetic layer in contact to a heavy non-magnetic metal, such as Néel-type domain walls and skyrmions, have been studied intensively because of their potential for future nanomagnetic devices. The Dyzaloshinskii-Moriya interaction (DMI) is an essential phenomenon for the formation of such chiral spin textures. In spite of recent theoretical progress aiming at understanding the microscopic origin of the DMI, an experimental investigation unravelling the physics at stake is still required.

Hund's Rule-Driven Dzyaloshinskii-Moriya Interaction at 3d-5d Interfaces.

Using relativistic first-principles calculations, we show that the chemical trend of the Dzyaloshinskii-Moriya interaction (DMI) in 3d-5d ultrathin films follows Hund's first rule with a tendency similar to their magnetic moments in either the unsupported 3d monolayers or 3d-5d interfaces. We demonstrate that, besides the spin-orbit coupling (SOC) effect in inversion asymmetric noncollinear magnetic systems, the driving force is the 3d orbital occupations and their spin-flip mixing processes with the spin-orbit active 5d states control directly the sign and magnitude of the DMI. The magnetic chirality changes are discussed in the light of the interplay between SOC, Hund's first rule, and the crystal-field splitting of d orbitals.

Pseudodirect to Direct Compositional Crossover in Wurtzite GaP/InGaP Core-Shell Nanowires.

Thanks to their uniqueness, nanowires allow the realization of novel semiconductor crystal structures with yet unexplored properties, which can be key to overcome current technological limits. Here we develop the growth of wurtzite GaP/InGaP core-shell nanowires with tunable indium concentration and optical emission in the visible region from 590 nm (2.1 eV) to 760 nm (1.

-asymmetric spin-splitting at the interface between transition metal ferromagnets and heavy metals.

We systematically investigate the spin-orbit coupling-induced band splitting originating from inversion symmetry breaking at the interface between a Co monolayer and 4 (Tc, Ru, Rh, Pd, and Ag) or 5 (Re, Os, Ir, Pt, and Au) transition metals. In spite of the complex band structure of these systems, the odd-in- spin splitting of the bands displays striking similarities with the much simpler Rashba spin-orbit coupling picture. While we do not find salient correlations between the interfacial magnetic anisotropy and the odd-in- spin-splitting of the bands, we establish a clear connection between the overall strength of the band splitting and the charge transfer between the -orbitals at the interface.

Optical Properties of Strained Wurtzite Gallium Phosphide Nanowires.

Wurtzite gallium phosphide (WZ GaP) has been predicted to exhibit a direct bandgap in the green spectral range. Optical transitions, however, are only weakly allowed by the symmetry of the bands. While efficient luminescence has been experimentally shown, the nature of the transitions is not yet clear.

Oxygen-enabled control of Dzyaloshinskii-Moriya Interaction in ultra-thin magnetic films.

The search for chiral magnetic textures in systems lacking spatial inversion symmetry has attracted a massive amount of interest in the recent years with the real space observation of novel exotic magnetic phases such as skyrmions lattices, but also domain walls and spin spirals with a defined chirality. The electrical control of these textures offers thrilling perspectives in terms of fast and robust ultrahigh density data manipulation. A powerful ingredient commonly used to stabilize chiral magnetic states is the so-called Dzyaloshinskii-Moriya interaction (DMI) arising from spin-orbit coupling in inversion asymmetric magnets.

Structure, energetics, and electronic states of III-V compound polytypes.

Recently several hexagonal polytypes such as 2H, 4H, and 6H have been discovered for conventional III-V semiconductor compounds in addition to the cubic 3C zinc-blende polytype by investigating nanorods grown in the [111] direction in different temperature regimes. Also III-mononitrides crystallizing in the hexagonal 2H wurtzite structure under ambient conditions can be deposited in zinc-blende geometry using various growth techniques. The polytypic crystal structures influence the local electronic properties and the internal electric fields due to the spontaneous polarization in non-cubic crystals.

Direct band gap wurtzite gallium phosphide nanowires.

The main challenge for light-emitting diodes is to increase the efficiency in the green part of the spectrum. Gallium phosphide (GaP) with the normal cubic crystal structure has an indirect band gap, which severely limits the green emission efficiency. Band structure calculations have predicted a direct band gap for wurtzite GaP.