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This research study undertakes a bulk arrival single server queue rendering two-heterogeneous services with optional re-service, under Bernoulli vacation schedule and $N$-policy subject to a random breakdown of the service station. For this model, Laplace–Stieltjes transform of the system reliability function is obtained using the supplementary variable technique. Further, the performance measure mean time to first failure of the server is derived. Moreover, a detailed numerical investigation of the model is carried out to show the applicability of the model.

Ga₂O₃ has gained worldwide interests for next-generation power electronics because its large critical field strength stemming from an ultra-wide bandgap promises miniaturized circuits and systems with high conversion efficiency. Intense pursuit of Ga₂O₃ power devices stimulated by early demonstrations of high-voltage Ga₂O₃ field effect transistors (FETs) has brought about tremendous advancements in this new technology, whose strong radiation tolerance and high thermal stability also befit harsh-environment applications. In this paper, we review the various types of depletionand enhancement-mode Ga₂O₃ FETs — which have predominantly been lateral devices — for power switching and radiation-hard electronics. The development of vertical Ga₂O₃ transistors based on a low-cost, highly-manufacturable ion implantation doping process will also be discussed.

Graphene has brought forward a lot of new physics. One of them is the emergence of massless Dirac fermions in addition to the electrons and these features are new to physics. In this theoretical study, the signatures for quantum scar and the breakdown of universality in graphene are investigated with reference to the presence of these two types of fermions. Taking the graphene quantum dot (QD) potential as the confining potential, the radial part of Dirac equations are solved numerically. Concentrations of the two component eigen-wavefunctions about classical periodic orbits emerge as the signatures for the quantum scar. The sudden variations, in the ratio of the radial wave-functions (large and small components), R(g/f), with mass ratio $\kappa$ are the signatures for breakdown of universality in graphene. The breakdown of universality occurs for the states k = −1 and k = 1, and the state k = −1 is more susceptible to the breakdown of universality.

A critical evaluation of high-power electronics switching in semiconductor materials is made from the standpoint of performance, reliability, and commercial viability. This study takes into account recent experimental results obtained from the field-reliability study of silicon power MOSFETs in high-density power supplies where residual material defects present in the space charge region of the device were found to generate local micro plasma that eventually caused power MOSFETs to fail. Based on these results and commercial progress made to date in wide bandgap semiconductor technologies, it is suggested that silicon carbide (SiC) promises to be the preferred material for high-power electronics switching from cost, performance and reliability considerations — this assessment is further strengthened by the near-term potential for developing large-area, low-cost, and defect-free SiC bulk substrates and epitaxial layers. This conclusion is also supported by the feasibility and the need for vertical, MOS-controlled, bipolar power switches in compact and efficient megaWatt-level power converters in order to make transformational changes in the 21st century electrical transmission and distribution infrastructure.

A short review is presented of a recently developed computational approach which allows the study of the resistance noise over the full range of bias values, from the linear regime up to electrical breakdown. Resistance noise is described in terms of two competing processes in a random resistor network. The two processes are thermally activated and driven by an electrical bias. In the linear regime, a scaling relation has been found between the relative variance of resistance fluctuations and the average resistance. The value of the critical exponent is significantly higher than that associated with 1/f noise. In the nonlinear regime, occurring when the bias overcomes the threshold value, the relative variance of resistance fluctuations scales with the bias. Two regions can be identified in this regime: a moderate bias region and a pre-breakdown one. In the first region, the scaling exponent has been found independent of the values of the model parameters and of the bias conditions. A strong nonlinearity emerges in the pre-breakdown region which is also characterized by non-Gaussian noise. The results compare well with measurements of electrical breakdown in composites and with electromigration experiments in metallic lines.

Good breakdown strength is an important feature for the selection of dielectric materials, especially in high-voltage engineering. Although nanocomposites have been shown to possess many promising dielectric properties, the breakdown strength of nanocomposites is often found to be negatively affected. Recently, imposing nonisothermal crystallization processes on polyethylene blends has been demonstrated to be favorable for breakdown strength improvements of dielectric materials. In an attempt to increase nanocomposites’ voltage rating, this work reports on the effects of nonisothermal crystallization (fast, moderate and slow crystallizations) on the structure and dielectric properties of a polyethylene blend (PE) composed of 80% low density polyethylene and 20% high density polyethylene, added with silicon dioxide (SiO₂) and silicon nitride (Si₃N₄) nanofillers. Through breakdown testing, the breakdown performance of Si₃N₄-based nanocomposites was better than SiO₂-based nanocomposites. Since nanofiller dispersion within both nanocomposite systems was comparable, the enhanced breakdown performance of Si₃N₄-based nanocomposites is attributed to the surface chemistry of Si₃N₄ containing less hydroxyl groups than SiO₂. Furthermore, the breakdown strength of SiO₂-based nanocomposites and Si₃N₄-based nanocomposites improved, with the DC breakdown strength increasing by at least 12% when both the nanocomposites were subjected to moderate crystallization rather than fast and slow crystallizations. This is attributed to changes in the underlying molecular conformation of PE in addition to water-related effects. These results suggest that apart from changes in the nanofiller surface chemistry, changes in the underlying molecular conformation of polymers are also important to improve the breakdown performance of nanocomposites.

Ga₂O₃ has gained worldwide interests for next-generation power electronics because its large critical field strength stemming from an ultra-wide bandgap promises miniaturized circuits and systems with high conversion efficiency. Intense pursuit of Ga₂O₃ power devices stimulated by early demonstrations of high-voltage Ga₂O₃ field effect transistors (FETs) has brought about tremendous advancements in this new technology, whose strong radiation tolerance and high thermal stability also befit harsh-environment applications. In this paper, we review the various types of depletion-and enhancement-mode Ga₂O₃ FETs — which have predominantly been lateral devices — for power switching and radiation-hard electronics. The development of vertical Ga₂O₃ transistors based on a low-cost, highly-manufacturable ion implantation doping process will also be discussed.

The flow near the axis of slender vortices is investigated with particular emphasis on the deceleration of the axial flow, leading to a stagnation point and bursting or breakdown of the vortex. The Euler equations are reduced for steady, inviscid, incompressible, axially symmetric flow in a stream tube of small radius. The angular velocity is found to be directly proportional to the axial velocity component, implying that a deceleration of the axial flow can cause the angular velocity to vanish and breakdown to occur. The extension of the analysis to viscous incompressible flow identifies a thin viscous layer immediately upstream of the stagnation point, its thickness being inversely proportional to the Reynolds number. An approximate solution for the viscous flow shows that the angular velocity does not vanish at the stagnation point of the axial flow. The results are compared with experimental and numerical data of the recent literature.