Electronic Topology Research Articles

Correction: Conceptual design of tetraazaporphyrin- and subtetraazaporphyrin-based functional nanocarbon materials: electronic structures, topologies, optical properties, and methane storage capacities.

Correction for 'Conceptual design of tetraazaporphyrin- and subtetraazaporphyrin-based functional nanocarbon materials: electronic structures, topologies, optical properties, and methane storage capacities' by Rodion V. Belosludov et al., Phys. Chem. Chem. Phys., 2016, 18, 13503-13518.

Efficient Objective Metric Tool for Medical Electrical Device Development: Eye Phantom for Glaucoma Diagnosis Device

Developing electronic medical devices is challenging. Simulations or in vivo experiments are not sufficient to obtain pertinent comparisons between potential design options. This paper presents a new artificial tool allowing objective comparisons between electronic device topologies. The main idea is to build a tool which is sensitive to targeted biological parameters only. These tools are generally called phantoms. The phantom presented in this paper is dedicated to IntraOcular Pressure (IOP) Measurement devices used in glaucoma diagnosis and treatment. It is called Biomechanical Eye Emulator (BEE). The BEE emulates the main biomechanical parameters influencing the IOP measurements. Because it is not sensitive to the living context, the BEE is the most efficient tool to investigate the best sensor design. BEE specifications are defined to be as close as possible to chosen models (humans or animals). Its efficiency is shown with a case study on rabbits. The results clearly demonstrate the BEE phantoms efficacy in providing objective assessment metrics during the sensor design process.

Wavelet Transform-Based <sc>EMI</sc> Noise Mitigation in Power Converter Topologies

This paper proposes a novel wavelet transform-based approach for electromagnetic interference (EMI) noise mitigation in power electronics topologies. The switching action of power semiconductor devices generates EMI in power converter modules which exceeds the noise limit set by the regulation of CISPR11. In order to cancel the EMI noise, the wavelet transform-based time-frequency localization approach has been used for generating a noise cancellation signal. The effectiveness of the proposed method has been evaluated in the terms of signal-to-noise ratio (SNR). Further, the effect of variance of the noise amplitude has been taken into consideration on the SNR. A relationship between the standard deviation, which is proportional to square root of the variance of the signal, and the SNR has been established. The proposed method has been implemented on the different power electronics topologies such as buck converter, boost converter, three-phase voltage source inverter, and Z-source inverter-based ac drive. The proposed method achieves the reduction of noise level below the safe limit set by CISPR11.

Theoretical study of anisotropic structural, electronic, mechanical and thermodynamic properties of rare-earth (R = Y, La) oxysulfides

The anisotropic structural, electronic, mechanical and thermodynamic properties of rare-earth (R=Y, La) oxysulfides are calculated by first-principles using density functional theory. From the calculated electronic structure and electron density topology, we find that the crystal structure of R2O2S is dominated by strong polar RO and RS bonds, and the ionic bond is the main bonding mechanism. The negative formation enthalpies imply that the formation of R2O2S from reactants (R2O3+H2S) is energetically favorable. The two oxysulfides show obvious anisotropy in elastic properties along different crystallographic directions, where Young's modulus shows stronger anisotropy than bulk modulus. The anisotropy in sound velocity is obtained by solving the Christoffel equation, the sound modes are isotropic at the basal plane (x-y plane), and weak anisotropy is seen on (100) crystallographic plane. The temperature dependence of volumetric TECs of both oxysulfides are similar, and the linear TECs in [001] direction are slightly higher than that of the [100] direction. At room temperature, the computed average linear TECs for Y2O2S and La2O2S are 9.5×10−6K−1 and 9.4×10−6K−1, respectively. Using Slack's model, it is found that thermal conductivities are 10.1 and 5.3W/mK in a range from 300K to 1500K for Y2O2S and La2O2S, respectively.

Electron–phonon metamaterial featuring nonlinear tri-interleaved piezoelectric topologies and its application in low-frequency vibration control

This article proposes a nonlinear tri-interleaved piezoelectric topology based on the synchronized switch damping on inductor (SSDI) technique, which can be applied to phononic metamaterials for elastic wave control and effective low-frequency vibration reduction. A comparison of the attenuation performance is made between piezoelectric phononic metamaterial with distributed SSDI topology (each SSDI shunt being independently connected to a single piezoelectric element) and piezoelectric phononic metamaterial with the proposed electronic topology. Theoretical results show excellent band gap hybridization (near-coupling between Bragg scattering mechanism and wideband resonance mechanism induced by synchronized switch damping networks in piezoelectric phononic metamaterials) with the proposed electronic topology over the investigated frequency domain. Furthermore, piezoelectric phononic metamaterials with proposed electronic topology generated a better low-frequency broadband gap, which is experimentally validated by measuring the harmonic response of a piezoelectric phononic metamaterial beam under clamped–clamped boundary conditions.

Sizing standalone battery charging systems based on Photovoltaic (PVTCP) Temperature Crossing Points using Voltage Source Photovoltaic Model (VSPVM)

Rural and semi-rural communities in third world countries harness solar energy mostly by using standalone Photovoltaic (PV) battery charging systems. Basic electronics circuits that do not include direct current to direct current (DC-DC) voltage converters are employed. These provide raw voltage levels from the solar PV modules that sometimes charge batteries insufficiently, leading to shorter battery lives. By modelling the solar PV module using a voltage source circuit representation, the effects of temperature on the PV module voltage could easily be illustrated to these rudimentary trained communities that deal mostly with voltage sources and not current sources. A Voltage Source PV Model (VSPVM) was developed from the well understood PV cell mathematical model. Microsoft Excel (MSE) was used as the data fitting environment and the PSpice environment was used to capture the electronic circuit topology proposed for the VSPVM. Validating the model against experimental data fitted maximum power points within 5% of the experimental data. Observations made on I-V characteristics plotted on the same graph showed interesting patterns of crossing points referred to here as Photovoltaic Temperature Crossing Points (PVTCP). A low temperature cluster and a high temperature cluster which were indicative of thresholds of some sort were observed. For hot climate regions, the power point voltage which exists between the two clusters could be considered as a guide to the possible range within which a PV battery charging system should operation.

Wireless power transfer technology using full‐bridge current‐fed topology for medium power applications

This paper studies, explores and analyses a wireless power transfer (WPT) system using current-fed power electronics topology for electric vehicles and battery charging applications. The main contribution is analysis, design, and implementation of a current-fed technology for WPT application. The required resonance in both the transmitter and receiver coils is parallel ( L )( C ) and series ( LC ) type, respectively. A detailed mathematical analysis and design have been reported. Stiff DC current at the input of the inverter limits the inverter switch current stress. Also, the inductor in DClink provides natural short-circuit protection during inverter fault. It is quite important in such application. Resonant converter facilitates soft-switching at turn-off of the transmitter side switches. Also, soft-commutation of rectifier diodes reduces reverse recovery loss. Mathematical analysis is verified by simulation results using PSIM 9.3. A 420 W proof-of-concept lab hardware prototype is developed and the experimental results are demonstrated to validate the mathematical analysis and simulation results. The maximum efficiency of DC-DC WPT stage obtained from the proof-of-concept lab-prototype is close to 90% with a coefficient of coupling 18%. It is suitable for solar-to-vehicle and single-phase residential slow charging.

Computational study of glucosepane–water and hydrogen bond formation: an electron topology and orbital analysis

The collagen protein provides tensile strength to the extracellular matrix in addition to localising cells, proteins and protein cofactors. Collagen is susceptible to a build up of glycation modifications as a result of an exceptionally long half-life. Glucosepane is a collagen cross-linking advanced glycation end product; the structural and mechanical effects of glucosepane are still the subjects of much debate. With the prospect of an ageing population, the management and treatment of age-related diseases is becoming a pressing concern. One area of interest is the isolation of hydrated glucosepane, which has yet to be reported at an atomistic level. This study presents a series of glucosepane–water complexes within an implicit aqueous environment. Electronic structure calculations were performed using density functional theory and a high level basis set. Hydrogen bonds between glucosepane and explicit water were identified by monitoring changes to covalent bonds, calculating levels of electron donation from Natural Bonding Orbital analysis and the detection of bond critical points. Hydrogen bond strength was calculated using second-order perturbation calculations. The combined results suggest that glucosepane is very hydrophilic, with the imidazole feature being energetically more attractive to water than either hydroxyl group, although all hydrogen bonds, regardless of bond strength, were electrostatic in nature. Our results are in growing support of an earlier hypothesis that cross-links may result in an increase in interstitial water retention, which would permit the collagen fibril to swell, thereby potentially affecting the tensile and compression properties and biological function of connective tissues.

The interaction strength of intermolecular systems formed by NaH⋯2(HF) and NaH⋯4(HF): Hydrogen bonds, dihydrogen bonds and halogen–hydride bonds

In this paper, a theoretical study of the molecular properties of NaH⋯2(HF) and NaH⋯4(HF) complexes is reported. Based on MP2/6-311++G(d,p) calculations, the dihydrogen bonds (H⋯H), hydrogen bonds (F⋯H) and halogen-hydride bonds (F⋯Na) of these intermolecular systems were fully characterized. The characterization involved the following procedures: the examination of structural parameters, analysis of vibration modes such as frequencies shifted to red or blue in the infrared spectrum, modeling of the electronic topology, quantification of the cooperative energy followed by charge transfer and, finally, natural bond orbital analysis. The results show short intermolecular distances with high electronic density, while the stretch frequencies of the proton donors and acceptors are unusually shifted, and some values reach 1000 cm −1 . When all subunits of the complexes are taken into account, in this case the NaH and HF molecules, the high value for the strength of the H⋯H dihydrogen bond in NaH⋯2(HF) suggests the formation of an additional subpart, i.e., the H 2 molecule.

Valence charge density of multi-doped Mg2Si thermoelectric materials from maximum entropy method analysis

The valence electron topologies of Mg2Si thermoelectric materials multi-doped with Al, Zn and Sb have been determined by the Maximum Entropy Method (MEM) using synchrotron X-ray powder diffraction data. In spite of the very low concentrations, expansion was observed in the cubic unit cells of the doped samples. Using pure Mg2Si as a reference, charge density difference maps revealed qualitative features on the distributions of the electrons contributed by the doped atoms. The presence of excess electrons shows all doped samples are n-type semiconductors and they are shared among the atomic sites. We evaluated the reliability of the MEM calculated charge density by considering the effect of successively increasing the number of high angle Bragg reflections used in the analysis on the diffraction pattern of a single doped Al–Mg2Si sample.

N-type conductivity in Si-doped amorphous AlN: an ab initio investigation

We report the electronic structure and topology of a heavily Si-doped amorphous aluminium nitride (Al37.5Si12.5N50) using ab initio simulations. The amorphous Al37.5Si12.5N50 system is found to be structurally similar to pure amorphous aluminium nitride. It has an average coordination number of about 3.9 and exhibits a small amount of Si–Si homopolar bonds. The formation of Si–Al bonds is not very favourable. Electronic structure calculations reveal that the Si doping has a negligible effect on the band gap width but causes delocalization of the valence band tail states and a shift of the Fermi level towards the conduction band. Thus, amorphous Al37.5Si12.5N50 alloys show n-type conductivity.

Five-Level Unidirectional T-Rectifier for High-Speed Gen-Set Applications

Multilevel power electronic topologies are being proposed in the recent technical literature for use in power generating units, especially when the reduction in the power filter overall dimensions and the lowering of current and voltage waveform ripple and total harmonic distortion are considered of primary importance. This is the case of high-speed gen-set units, where recent design techniques on high rotational speed permanent-magnet synchronous generators (PMSGs) have significantly reduced the inductance even for industrial voltage rated applications. This paper deals with a five-level unidirectional T-rectifier (5L T-RECT); the proposed topology is theoretically investigated, and simulation results and losses analysis are achieved with reference to an insulated-gate bipolar transistor (IGBT) phase-leg module which has been manufactured on purpose and tested.

Pressure-induced phase transition in Bi2Se3 at 3 GPa: electronic topological transition or not?

In recent years, a low pressure transition around GPa exhibited by the -type 3D topological insulators is attributed to an electronic topological transition (ETT) for which there is no direct evidence either from theory or experiments. We address this phase transition and other transitions at higher pressure in bismuth selenide (Bi2Se3) using Raman spectroscopy at pressure up to 26.2 GPa. We see clear Raman signatures of an isostructural phase transition at GPa followed by structural transitions at ∼10 GPa and 16 GPa. First-principles calculations reveal anomalously sharp changes in the structural parameters like the internal angle of the rhombohedral unit cell with a minimum in the c/a ratio near GPa. While our calculations reveal the associated anomalies in vibrational frequencies and electronic bandgap, the calculated invariant and Dirac conical surface electronic structure remain unchanged, showing that there is no change in the electronic topology at the lowest pressure transition.

Conceptual design of tetraazaporphyrin- and subtetraazaporphyrin-based functional nanocarbon materials: electronic structures, topologies, optical properties, and methane storage capacities.

A large variety of conceptual three- and fourfold tetraazaporphyrin- and subtetraazaporphyrin-based functional 3D nanocage and nanobarrel structures have been proposed on the basis of in silico design. The designed structures differ in their sizes, topology, porosity, and conjugation properties. The stability of nanocages of Oh symmetry and nanobarrels of D4h symmetry was revealed on the basis of DFT and MD calculations, whereas their optical properties were assessed using a TDDFT approach and a long-range corrected LC-wPBE exchange-correlation functional. It was shown that the electronic structures and vertical excitation energies of the functional nanocage and nanobarrel structures could be easily tuned via their size, topology, and the presence of bridging sp(3) carbon atoms. TDDFT calculations suggest significantly lower excitation energies in fully conjugated nanocages and nanobarrels compared with systems with bridging sp(3) carbon fragments. Based on DFT and TDDFT calculations, the optical properties of the new materials can rival those of known quantum dots and are superior to those of monomeric phthalocyanines and their analogues. The methane gas adsorption properties of the new nanostructures and nanotubes generated by conversion from nanobarrels were studied using an MD simulation approach. The ability to store large quantities of methane (106-216 cm(3) (STP) cm(-3)) was observed in all cases with several compounds being close to or exceeding the DOE target of 180 cm(3) (STP) cm(-3) for material-based methane storage at a pressure of 3.5 MPa and room temperature.

Analysis and Comparison of Power Electronic Converters for Conventional and Toroidal Switched Reluctance Machines

Different power electronic converter topologies are introduced in this paper for both Conventional Switched Reluctance Machine (CSRM) and Toroidal Switched Reluctance Machine (TSRM) drive systems. Their commutation, switch and diode currents, power losses, and efficiencies under over modulation operation are analyzed and compared for converter characteristics study, performance evaluation and topology selection for CSRM and TSRM drive systems. The switch and diode silicon volumes required for each CSRM and TSRM drives are also compared according to their corresponding currents at the equivalent machine torque versus speed operating points.

A Vanadium Chalcogenide Dicubane

AbstractThe discovery of novel transition metal cubane clusters with different electron counts and topologies is of considerable importance due to the prevalence of this structure type in catalytic proteins. Here, we report the solvothermal synthesis and full characterization of [V7S8Cl2(en)8]Cl4 (en = ethylenediamine), the first early transition metal dicubane cluster. Electron paramagnetic resonance and magnetic susceptibility measurements show that the cluster has one unpaired electron localized on a single V4+, which according to DFT simulations is the central bridging vanadium. The remaining V3+ atoms feature significant metal–metal bonding.

Type II InAs/GaAsSb quantum dots: Highly tunable exciton geometry and topology

External control over the electron and hole wavefunctions geometry and topology is investigated in a p-i-n diode embedding a dot-in-a-well InAs/GaAsSb quantum structure with type II band alignment. We find highly tunable exciton dipole moments and largely decoupled exciton recombination and ionization dynamics. We also predicted a bias regime where the hole wavefunction topology changes continuously from quantum dot-like to quantum ring-like as a function of the external bias. All these properties have great potential in advanced electro-optical applications and in the investigation of fundamental spin-orbit phenomena.

Detecting Band Inversions by Measuring the Environment: Fingerprints of Electronic Band Topology in Bulk Phonon Linewidths.

The interplay between topological phases of matter and dissipative baths constitutes an emergent research topic with links to condensed matter, photonic crystals, cold atomic gases, and quantum information. While recent studies suggest that dissipative baths can induce topological phases in intrinsically trivial quantum materials, the backaction of topological invariants on dissipative baths is overlooked. By exploring this backaction for a centrosymmetric Dirac insulator coupled to phonons, we show that the linewidths of bulk optical phonons can reveal electronic band inversions. This result is the first known example where topological phases of an open quantum system may be detected by measuring the bulk properties of the surrounding environment.

Cleaner Coal: Improving Energy Efficiency at a Coal Preparation Plant in Western Canada

In an environment of constantly cyclical mineral market prices, operators of sites in the global mining industry are challenged to continuously improve processes to remain competitive with their peers. Although not necessarily a priority in the past, the issue of energy-efficiency project upgrades has moved to the forefront of mine operations. The dual benefits of serving as a means of offsetting rising energy costs and reducing emissions to reduce the environmental footprint are compelling. This article is a case study of one such energy-efficiency project recently implemented at a coal preparation plant in western Canada. The project began with a coal dryer energy efficiency feasibility study (EEFS) performed by a global energy services engineering company. Solicitation for the EEFS was supported by the local utility company serving the mine site, which funded the cost of the research. This article will review the analysis methods used and the recommendations included in the study and then describe site implementation of one of the key deliverables of the EEFS: a proposed plan to install a 6,000-hp medium-voltage adjustable frequency drive (AFD) to improve control of the main coal dryer exhaust fan. This article will also describe the unique AFD selected for installation for this load, including an overview of the power electronics topology and the resulting performance in delivering improved energy efficiency and process improvements. This upgrade ultimately ensured that energy and operational costs were reduced while the coal preparation plant delivered a superior end product to its customers.

Topological Bloch bands in graphene superlattices

We outline a designer approach to endow widely available plain materials with topological properties by stacking them atop other nontopological materials. The approach is illustrated with a model system comprising graphene stacked atop hexagonal boron nitride. In this case, the Berry curvature of the electron Bloch bands is highly sensitive to the stacking configuration. As a result, electron topology can be controlled by crystal axes alignment, granting a practical route to designer topological materials. Berry curvature manifests itself in transport via the valley Hall effect and long-range chargeless valley currents. The nonlocal electrical response mediated by such currents provides diagnostics for band topology.