Ravindra P. Joshi

Photoelectron emission provides high electron current densities required in various applications. In this context, the necessary numerical analysis involving carrier transport can be somewhat tedious as both the thermalized and photogenerated subpopulations must be tracked until they reach the emitting surface. Here, an alternative evaluation utilizing the lucky-drift electron (LDE) concept for field-dependent photoemission current density is carried out. Simulations are performed to include carrier transport in a metallic emitter, consistent with the internal potential and related work function (Φ) based on density-functional theory and a modified Fowler–Nordheim treatment. The results show very close agreement between the LDE approximation and full Monte Carlo analysis for the calculated photo-assisted field-emission current density.

The proliferation of wireless communications, high-power microwave (HPM) sources, radar, and other microwave technology has necessitated research into potential HPM bioeffects. Here we present a multi-physics simulation study to probe the possible generation of thermoacoustic pressure waves from incident electromagnetic pulses, in a layered dielectric representation of the human head. The model is designed to offer flexibility with customizable pulse length, rise and fall times, repetition rates, applied electric field value, and user-defined directional orientation. Our results suggest that pressure could be generated at the center of the intra-cranial region, qualitatively in keeping with some reports in the literature. Continuous pulsing is seen to lead to pressure build-up in the head close to the location of incident stimulus; while with short-pulsed stimulation, the effects are predicted to be greater at the center of the intra-cranial region. The results also show that with decreases in pulse length, while the absolute pressure amplitude is enhanced, the disturbance becomes less oscillatory in nature.

Evaluations of the current output from metal emitter arrays with a hexagonal lattice arrangement are carried out based on kinetic simulations. Geometric field enhancements with shielding and the presence of workfunction (ϕ) variations are included. Electron emission is treated using modified field emission theory, with ϕ variability based on a simple patchwork model. Results for arrays with different numbers of metal emitters show that for a given mean ϕ value, the greatest currents result for structures having the largest variability. Furthermore, it may be desirable to incorporate ϕ fluctuations in cathodes at the central zone of emitter arrays to mitigate screening effects and enhance currents. The results also indicate lowest emittance in the case of cathode surfaces with minimal ϕ variability. As the chosen technique is general, related aspects such as heating effects, a more comprehensive electro-thermal model of electron emission, or Wigner-based electron cathodic transport for a more complete analysis of photoemission could be included in future work.

This paper presents a robust chance-constrained scheduling model for medium voltage (MV) networks with distributed energy resources (DERs) including photovoltaic (PV) panels, energy storage (ES) systems, and distributed generators (DGs), in order to tackle uncertainties in PV generation and energy demand. The fast penetration of solar PV systems into MV and low-voltage (LV) electric grids has introduced higher operating complexity because of the intermittent character of renewable power generation, thus requiring sophisticated optimization techniques in the control of efficient power systems. The optimal power flow (OPF) methodology is used for enhancing control variables such as generation dispatch, voltage magnitudes, and power flows. The methodology transitions from classical deterministic OPF to hybrid robust-chance-constrained programming with incorporation of ES systems for mitigating PV variability and enhancing system flexibility. Simulations on a modified IEEE 33-bus test system benchmarks eight case studies, ranging from deterministic to stochastic and robust-chance-constrained programming. Results indicate the proposed framework increases loadability, e.g. by up to 34% in Case 7; reduces operational costs in Case 5 by 93.7% compared to Case 4; and enhances voltage stability, e.g., minimum 0.9 pu in Case 5. Analyses of the results also reveal that the presented strategic coordination framework enables efficient power transaction with the MV grid. Moreover, the integration of energy storage systems alone enhances the network’s load factor from 58.54% to 62.67% and reduces peak demand by approximately 22%. With the mixture of robust optimization’s reliability and chance-constrained flexibility, this study presents a scalable uncertainty-aware solution for MV-LV grids.

Studies of metallic field emission devices during operation have reported fluctuations in current and local luminosity across the emitting surface that suggest a time-dependent evolution of surface structure and morphology. One possibility is the growth of surface nanoprotrusions (NPs) driven by high Maxwell stress arising from the externally applied electric field. This aspect is probed through three-dimensional, time-dependent molecular dynamics simulations for a quantitative predictive analysis. Our results indicate NP growth for electric fields at levels of 5 × 108 V/m or higher. Material ejection from NPs is also shown to be likely for high fields acting over an extended duration. The trends agree qualitatively with reports in the literature, demonstrating the role of grain boundaries as an enabling mechanism, showing that NP growth is synergistically strengthened by the presence of surface voids, and the possibility of dynamic current fluctuations.

This paper proposes a centralized energy management system for low voltage (LV) distribution networks. The main contribution of this model is to manage the energy serving at the local energy communities in the presence of electric vehicle supply equipment (EVSE). Unlocking the demand response potential by the EVSE at the distribution network with the contribution of the active residential prosumers has been investigated in this study under different operational planning scenarios. The developed model is based on the multi-temporal optimal power flow (MTOPF) concept while the unbalanced nature of LV networks has been addressed using unbalanced power flow equations. The aggregator can effectively manage the optimal charging of electric vehicles (EVs) by home and public chargers available at the distribution network. Simulation results on a modified unbalanced LV network illustrate that the optimal operation of EVSE minimizes the electricity costs of end-users. The simulation results show that the operating costs and systems losses reduce by 9.22% and 43.45%, respectively. These results have been obtained considering the switching actions and 100% PV power generation index using the presented MV-LV coordinated operational model. Besides, the energy storage systems improve the peak-to-average (PAR) ratio by 9.87%.

Devices based on electrical stimulation are in common use for a variety of therapeutic bio-applications, including, but not limited to, neuro-prosthetics, pain management or even in situ local anesthetic modalities. Many require the use of multielectrode systems to selectively activate a group of nerves. In this context, a modeling study is carried out to probe some of the details of nerve activation resulting from multielectrode excitation. In particular, aspects such as threshold stimulus currents, their variation with the number of electrodes used, dependence on nerve radii, and the possibility of blocking an action potential (AP) have been quantitatively analyzed. The injection currents needed to initiate an AP are shown to decrease as the number of stimulating electrodes increases. It is also demonstrated that blocking AP propagation in a nerve segment could be achieved more efficiently at lower magnitudes of the interruption signal if more electrodes in an electrical excitation array were to be used. This result is important and would have practical relevance since the lower intensity external signals indicate a safer and more reliable approach to both AP launches and possible AP blockages.

Outgassing remains an important issue in the context of high-power microwave system operation as it can lead to several undesirable outcomes. Hence, suppression or containment of this phenomena becomes a germane issue. Here, a possible solution strategy based on quasi- isentropic compression (QIC) is probed with quantitative predictions based on molecular dynamics (MD) simulations. Using copper with hydrogen gaseous impurity as an example anode for MD analyses, our results show that a strong and short pressure ramp applied at one surface can lead to a herding of hydrogen atoms toward the opposite face. Such gaseous impurity gathering could set the stage for the efficient surface treatment and cleaning. Additionally, it is shown that upon compression, the surface becomes denser and resistant to subsequent diffusive uptake of hydrogen atoms from the environment, thus, effecting a surface seal. Future work could be aimed to probe QIC for electrode materials with a suitable coating.