We consider three-dimensional Lorentzian Egorov and epsilon-spaces and show that the existence of proper biharmonic helices in these manifolds is highly constrained and closely tied to the causal character of the Frenet frame. In particular, we prove that no proper biharmonic helices exist in Egorov spaces unless the space is flat and the normal vector is spacelike. Furthermore, we establish that no proper biharmonic helices exist in threedimensional epsilon-spaces.
Power converters are essential for solar energy systems but achieving over 96% efficiency at 1 kW and 300 kHz with compact magnetic and EMC compliance remains challenging for high-power-density PV applications. This study presents the design, modeling, and experimental validation of a 1 kW two-phase interleaved boost converter operating from 12 V input to 48 V/20 A output, featuring a single EE32 Litz-wound coupled-core inductor with coupling coefficient k = −0.475 that reduces per-phase current ripple to just 120 mA (0.6% relative) at full load, a load-selective active zero-current switching (ZCS) circuit activated above 5 A threshold via DCR sensing to minimize switching losses without light-load penalties, and digital peak-current control with 2P2Z compensator implemented on an XMC4200 microcontroller, ensuring robust stability. Experimental results demonstrate peak efficiency of 98.6% at approximately 190 W load, full-load efficiency of approximately 96% with total losses limited to 40 W dominated by conduction rather than switching, thermal rise below 80 °C on key components, voltage regulation with less than 1% deviation down to 2 A minimum load, and full compliance with electromagnetic compatibility standards, including EN 55014-1/2 and EN 61000-4-2 ESD testing. The novel integration of selective ZCS, single-core magnetic, and high-frequency operation outperforms prior interleaved boost converters, which typically achieve 94–97% peak efficiency at lower switching frequencies of 20–100 kHz using multiple inductors or complex always-active resonant networks, making this solution particularly suitable for compact photovoltaic micro-converters, electric vehicles, and industrial power supplies requiring high efficiency, reliability, and regulatory compliance.
Tools inevitably degrade over time, with lifespans varying based on material and usage.To mitigate this, thermochemical treatments such as boriding are employed. This process forms a boride layer with favorable tribological and mechanical properties. Generally, depending on the processing conditions, the layer may resultin either a mono-phased Fe2B or a bi-phased FeB/Fe2B structure.This study examines a mono-phased Fe2B layer formed by powder pack boriding of Armco Iron.The objective is to predict the thickness of this layer using a linear approach with minimal variables, and to compare the predictions with a more complex approach requiring additional parameters. Results show that both models yield similar predictive capabilities within the available interval, validating the linear model. However, the linear approach shows divergence when applied beyond the investigated interval, indicating limitations in its generalizability.
In this work, a recent version of the full potential linear muffin-tin orbitals (FP-LMTO) method was employed, using the local density approximation (LDA) within the framework of density functional theory (DFT). This approach was applied to study the structural, electronic and elastic behavior of the potassium iodide (KI) compound under pressure. The calculated structural parameters exhibit strong agreement with available theoretical and experimental data. The RS phase was identified as the most stable structure for KI material. The phase transition from NaCl-type (B1) to CsCl-type (B2) phase occurs at pressure of 1.633 GPa, which is quite consistent with the experimental values. Furthermore, the band structure of KI revealed a wide-band gap semiconductor behavior across all examined phases. The obtained bulk modulus values were relatively low, suggesting weak resistance to fracture. The elastic constants for KI in RS, CsCl, ZnS, HCP, and WZ structures were determined and found to meet Born’s stability conditions. We esteem, there is no values available in the literature on the elastic constants for KI in CsCl, ZnS and WZ phases. All analyzed structures displayed ductile characteristics and ionic bonding features. Additionally, anisotropic properties were observed in all phases. The compound’s stiffness was evaluated using Poisson’s ratio and Cauchy’s pressure. Results indicated that the CsCl phase is the most rigid among the studied configurations.
Electrochemical impedance spectroscopy (EIS) is a very powerful tool for exploitation as a rich source of Proton Exchange Membrane Fuel Cell (PEMFC) diagnostic information.A primary goal of this work was to develop a suitable PEMFC impedance model, which can be used in the analysis for flooding and drying of fuel cell. For this one a novel optimization method based on factorial Design methodology is used. It was applied for parametric analysis of electrochemical impedance Thus it is possible to evaluate the relative importance of each parameter to the simulation accuracy. Furthermore this work presents an analysis of the PEMFC impedance behavior in the case of flooding and drying.
