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Robust simulation is essential for reliable operation and planning of transmission and distribution power grids. At present, disparate methods exist for steady-state analysis of the transmission (power flow) and distribution power grid (three-phase power flow). Due to the non-linear nature of the problem, it is difficult for alternating current (AC) power flow and three-phase power flow analyses to ensure convergence to the correct physical solution, particularly from arbitrary initial conditions, or when evaluating a change (e.g. contingency) in the grid. In this paper, we describe our equivalent circuit formulation approach with current and voltage variables that models both the positive sequence network of the transmission grid and three-phase network of the distribution grid without loss of generality. The proposed circuit models and formalism enable the extension and application of circuit simulation techniques to solve for the steady-state solution with excellent robustness of convergence. Examples for positive sequence transmission and three-phase distribution systems, including actual 75k+ nodes Eastern Interconnection transmission test cases and 8k+ nodes taxonomy distribution test cases, are solved from arbitrary initial guesses to demonstrate the efficacy of our approach., Comment: Accepted manuscript for IEEE Transactions on Power Systems (under review). arXiv admin note: text overlap with arXiv:1711.01471

Abstract Colloids driven by phoresis constitute one of the main avenues for the design of synthetic microswimmers. For these swimmers, the specific form of the phoretic and hydrodynamic interactions dramatically influences their dynamics. Explicit solvent simulations allow the investigation of the different behaviors of dimeric Janus active colloids. The phoretic character is modified from thermophilic to thermophobic, and this, together with the relative size of the beads, strongly influences the resulting solvent velocity fields. Hydrodynamic flows can change from puller-type to pusher-type, although the actual flows significantly differ from these standard flows. Such hydrodynamic interactions combined with phoretic interactions between dimers result in several interesting phenomena in three-dimensional bulk conditions. Thermophilic dimeric swimmers are attracted to each other and form large and stable aggregates. Repulsive phoretic interactions among thermophobic dimeric swimmers hinder such clustering and lead, together with long- and short-ranged attractive hydrodynamic interactions, to short-lived, aligned swarming structures. Graphic Abstract

Recent advances have shown that the circuit simulation algorithms that allow for solving highly nonlinear circuits of over one billion variables can be applicable to power system simulation and optimization problems through the use of an equivalent circuit formulation. It was demonstrated that large-scale (80k+ buses) power flow simulations can be robustly solved, independent of the initial starting point. In this paper, we extend the electronic circuit-based G-min stepping homotopy method to power flow simulations. Preliminary results indicate that the proposed algorithm results in significantly better simulation runtime performance when compared to existing homotopy methods., Accepted for IEEE Conference on Environment, Electrical Engineering and I&CPS Europe, Genoa, Italy, June 2019

Simulating potential cascading failures can be useful for avoiding or mitigating such events. Currently, existing steady-state analysis tools are ill-suited for simulating cascading outages as they do not model frequency dependencies, they require good initial conditions to converge, and they are unable to distinguish between a collapsed grid state from a hard-to-solve test case. In this paper, we extend a circuit-theoretic approach for simulating the steady-state of a power grid to incorporate frequency deviations and implicit models for underfrequency and undervoltage load shedding. Using these models, we introduce a framework capable of robustly solving cascading outages of large-scale systems that can also locate infeasible regions. We demonstrate the efficacy of our approach by simulating entire cascading outages on more than 8000 nodes sample testcase., Presented in IEEE PES Innovative Smart Grid Technologies Europe Conference, Bucharest, Romania, 2019

An equivalent circuit formulation for power system analysis was demonstrated to improve robustness of Power Flow and enable more generalized modeling, including that for RTUs (Remote Terminal Units) and PMUs (Phasor Measurement Units). These measurement device models, together with an adjoint circuit based optimization framework, enable an alternative formulation to Power System State Estimation (SE) that can be solved within the equivalent circuit formulation. In this paper, we utilize a linear RTU model to create a fully linear SE algorithm that includes PMU and RTU measurements to enable a probabilistic approach to SE. Results demonstrate that this is a practical approach that is well suited for real-world applications., Comment: 19th IEEE International Conference on Environment and Electrical Engineering, 2019, Genova, Italy

An Equivalent Circuit Programming (ECP) approach that expresses the optimality conditions of an optimization problem in terms of an equivalent circuit model and uses circuit simulation techniques to solve for an optimal solution, is applied to the state estimation problem for power systems. The benefits of using an equivalent circuit formulation for incorporating both Phasor Measurement Units (PMU) and Remote Terminal Units (RTU), as well as for reducing the nonlinearities of the state estimation problem was previously demonstrated. In this paper we further exploit the circuit nature of the state estimation problem to formulate not only the model but also the optimality conditions as an ECP problem. The efficiency and accuracy of our approach are demonstrated by estimating the states of large-scale power grids (80k+ buses)., Comment: Accepted for the 2019 Powertech Milan conference

Robust solving of critical large power flow cases (with 50k or greater buses) forms the backbone of planning and operation of any large connected power grid. At present, reliable convergence with applications of existing power flow tools to large power systems is contingent upon a good initial guess for the system state. To enable robust convergence for large scale systems starting with an arbitrary initial guess, we extend our equivalent circuit formulation for power flow analysis to include a novel continuation method based on transmission line (Tx) stepping. While various continuation methods have been proposed for use with the traditional PQV power flow formulation, these methods have either failed to completely solve the problem or have resulted in convergence to a low voltage solution. The proposed Tx Stepping method in this paper demonstrates robust convergence to the high voltage solution from an arbitrary initial guess. Example systems, including 75k+ bus test cases representing different loading and operating conditions for Eastern Interconnection of the U.S. power grid, are solved from arbitrary initial guesses.Interconnection of the U.S. power grid, are solved from arbitrary initial guesses.

Recent development of techniques that improve the convergence properties of power flow simulation have been demonstrated to facilitate scaling to large system sizes (80k+ buses). However, the problem remains to reliably identify cases that are infeasible, system configurations that have no solution. In this paper, we use the circuit theoretic approach based on adjoint networks to evaluate the feasibility of a power flow test case and further locate and quantify the source of infeasibility in the cases operating beyond the tip of the nose curve. By creating infeasibility current source models that are added to each node of the system model and further coupling each source to its corresponding node of the adjoint network, any locations of insufficient real or reactive power are captured by a non-zero response of the adjoint network. Furthermore, it is shown that the proposed joint simulation of power flow and its adjoint network models provide the optimally minimized currents that can be later utilized to inform corrective actions to restore the feasibility of power flow problems., Comment: Submitted manuscript for IEEE Transactions onSmart Grids (under review)

This paper describes how to utilize physics-based unified modeling of complex electric power systems in order to design a multi-layered interactive Smart Grid in a Room Simulator (SGRS). In this simulator, the dynamic response of a given interconnected grid is simulated and assessed as a family of interfaced sub-processes jointly evolving at different time-scales. Compared to state-of-the-art simulators, advantages of the SGRS are that it is scalable to large systems since it uses distributed computing and that it allows for privacy of different components since one object does not need to know the models or methods of another object. Standardized and transportable objects representing physical components at various degrees of temporal, spatial, and functional granularity are constructed by different users and added to the SGRS platform for future use by all. This allows users to simulate and assess the effect of the technology of interest to them, which makes the SGRS effective in supporting the deployment of new technologies with well-understood effects. Examples on the SRGS are described for simulating market-driven sub-processes and the fast dynamics sub-processes in response to market actions and/or to sudden hard-to-predict disturbances.

Ternary rare-earth metal scandate layers deposited using pulsed laser deposition (PLD) were studied as dielectrics for high-k applications. GdScO3, DyScO3 and LaScO3 blanket layers with different nominal thicknesses were deposited directly on 2-inch Si (100) substrates for physical characterizations and 2-inch substrates with a lateral SiO2 isolation structure, for capacitor formation with wet-etched electrodes. High- temperature X-ray diffraction (HT-XRD) and TEM reveal that DyScO3 and GdScO3 remain amorphous up to 1000C. The as- deposited DyScO3 layer on both 1nm chemical SiO2 and HF-last surface of Si shows good interface properties as revealed by C- V curves. The leakage current through the layers is comparable to or even lower than that through HfO2 layers of the same EOT. Material properties show sensitivity to annealing conditions.

Ternary oxides (GdScO 3 , DyScO 3 and LaScO 3 —in general RE ScO 3 whereas RE stands for rare earth) were studied as alternative high- κ -dielectrics. Thin amorphous films were deposited on Si (1 0 0) using pulsed laser deposition (PLD) with two different geometries (on-axis and off-axis). The films were characterized using Rutherford backscattering spectrometry (RBS), XRD, AFM, SEM and capacitors by CV and leakage current measurements. GdScO 3 and DyScO 3 remain in the amorphous phase while heating up to 1000 °C. The films produced in the on-axis-geometry are of higher quality concerning stoichiometry, morphology and electrical properties than the off-axis films. A composition close to the stoichiometry of RE ScO 3 is found. In summary, a film density of 95% of crystalline samples, a surface roughness of about 1 A RMS, a permittivity of about 20 and leakage current densities of 10 −8 A/cm 2 for a film thickness of 5 nm were achieved.

Thin films of rare-earth scandates (RE ScO"3) as well as multi-layers of scandates and titanates have been prepared using pulsed laser deposition. Epitaxial films were grown on SrRuO"3/SrTiO"3(100) as well as amorphous films on silicon substrates. The epitaxial films are investigated to measure the physical properties of the crystalline material. Electrical measurements (CV, leakage current) show for example high @e"r>20 for the scandates and @e"r>35 for the epitaxial and amorphous multi-layer films. A diffusion of the new materials into silicon is not observed.

Self-propelled phoretic colloids have recently emerged as a promising avenue for the design of artificial microswimmers. Here we show how systems of thermophobic dimeric swimmers can form swarms, in the sense of clusters with an ordered collective net motion. The interplay of attractive hydrodynamic with repulsive phoretic interactions leads to the formation of swarming structures with a flattened geometry in three-dimensional systems. The design of microfluidic devices and of bio-compatible microrobots can benefit from these dynamic and controllable systems.

The main factors of fine bubble aeration systems in uniform arrangement in clean water are the air flow rate, the depth of submergence of the diffusers, and the diffuser density. While the influence of the air flow rate on the oxygen transfer parameters is known, knowledge of the influence of the depth of submergence and the diffuser density on the specific oxygen transfer efficiency SOTE [%/m] and on the specific oxygen absorption SOA [g/m3·m at STP] is very limited. Both parameters are of great importance in dimensioning fine bubble aeration systems. Therefore, a literature review was conducted to show the influence of the diffuser submergence and density and the type of blower on oxygen transfer and aeration efficiency. The main review results are, that higher values of specific oxygen absorption can be obtained at higher diffuser density; secondly, the volumetric oxygen transfer rate VOTR [g/m3·h] is higher with increasing depth of submergence at the same air flow rate. Also it can be stated that with greater depth of submergence the specific oxygen absorption [g/m3·m at STP] is reduced. Dependent on the air flow rate and the pressure head, the energy consumption [Wh/m3·m at STP] of the blowers used in wastewater treatment plants is different. For example, the energy consumption varies from 4.3 [Wh/m3·m at STP] (positive displacement blower) to 3.0 [Wh/m3·m at STP] (turbo-compressors) at a pressure of 10 m and an air flow rate of 5,000 m3/h at STP. From the results of the literature review the following conclusions can be drawn: (1) High specific oxygen absorption values (SOA) [g/m3·m at STP] can be achieved applying shallow tanks, high diffuser densities and low specific air flow rates; (2) High aeration efficiencies (AE) [kg/kWh] can be obtained by applying high volumetric oxygen transfer rates and adequate selection of the blowers used at the wastewater treatment plants.

Rare earth scandate thin films (GdScO3 and DyScO3) were investigated with respect to future high-k applications. They were deposited on (100) silicon substrates using either pulsed laser deposition (PLD) or electron beam evaporation. The investigation of the films was done by means of Rutherford backscattering spectrometry, high-temperature X-ray-diffractometry, X-ray reflectometry, spectroscopic ellipsometry, transmission electron microscopy (TEM) and atomic force microscopy. For the electrical characterization capacitor stacks were prepared. Both materials show very promising characteristics independent from the deposition technique used. The films are stoichiometric and amorphous and exhibit a smooth surface (roughness RMS < 1 Å). The amorphous phase is stable up to 1000°C. The electrical characterization revealed featureless C-V-curves with a small hysteresis. From CET plots (CET = capacitance equivalent thickness) k-values between 20 and 23 could be extracted. The electron beam evaporation produces films with a better homogeneity and a thinner interfacial silicon dioxide and therefore a smaller CET value as confirmed by TEM. The leakage current density of the film with CET = 1.5 nm was as low as 7.7x10-4 A/cm2.

Gadolinium scandate thin films deposited on silicon substrates using electron beam evaporation were investigated. Measurements with Rutherford backscattering spectrometry, high temperature x-ray diffraction, x-ray reflectometry, transmission electron microscopy, and atomic force microscopy were performed. A stoichiometric transfer of material from the source to the substrate in high vacuum could be demonstrated. Homogeneous, amorphous, and smooth films (root mean square surface roughness < 1 A) stable up to 1000 degrees C were obtained. Electrical characterization of capacitor stacks revealed a dielectric constant of approximate to 23, C-V curves with small hysteresises and low leakage current densities (770 mu A/cm(2) for a capacitance equivalent thickness of 1.5 nm). (c) 2006 American Institute of Physics.