Search Results (351)

The simulation of modern wireless communication circuits remains challenging because of the coexistence of nonlinear behavior, heterogeneous subsystems, and widely separated time scales. This review presents a structured overview of advanced numerical methods for solving multitime partial differential–algebraic equations (MPDAEs) arising in circuit-level modeling of RF and microwave systems. Compared with previous survey papers, the main contribution of this work is to organize the literature according to the underlying numerical strategy, distinguishing purely time-domain, hybrid time–frequency, multidimensional frequency-domain, and circuit-block partitioning approaches. The reviewed methods show that multitime formulations can deliver substantial computational gains over conventional simulation techniques, particularly for multirate and multiscale circuits. Time-domain techniques are generally more robust for strongly nonlinear regimes, whereas frequency-domain and hybrid methods are often more efficient when the waveform can be represented with a limited number of harmonics. Circuit-block partitioning further improves efficiency by exploiting active and latent variables, but the computational complexity of MPDAE methods increases rapidly with the number of time scales, and their applicability becomes more limited for aperiodic or highly general multirate excitations. Overall, this review highlights both the strengths and the practical limitations of current MPDAE-based numerical approaches and identifies open challenges for future research. Full article

The increasing penetration of inverter-based renewable energy resources, especially photovoltaic (PV) systems, has decreased the available system inertia and introduced challenges in maintaining stable grid-forming operation. This paper presents a grid-forming photovoltaic multilevel inverter (MLI) with a modified delta-connected cascaded H-bridge (CHB) multilevel configuration. The proposed system decreases the number of semiconductor switches and provides inherent voltage balancing, while also achieving high power quality, rendering it suitable for grid-forming applications. Each H-bridge cell is connected to an isolated Cúk converter to enable maximum power point tracking (MPPT) of distributed PV modules, allowing for flexible and modular DC-side integration. The proposed MLI operates as a virtual synchronous generator. A control scheme is proposed to attain grid-forming capability, hence providing stable voltage and frequency support. Moreover, a DC-link voltage regulation strategy is also developed to maintain the DC-link voltage at the reference voltage. A detailed mathematical model is developed to characterize the associated dynamics of the proposed MLI and the control system with a grid interface. The model is built in the SIMULINK environment, and the simulation results are presented under variations in solar radiation and grid voltage disturbances to exhibit the functionality of the proposed system and the effectiveness of the control scheme in providing a well-damped frequency response and stable generated voltage and currents. The results demonstrate stable frequency regulation with a settling time of approximately 0.3 s, and the output current exhibits low harmonic distortion, with a Total Harmonic Distortion (THD) of about 0.53%. Simulation results show stable operation and confirm that the proposed approach is a competitive solution for PV-based grid-forming applications. Full article

The new projective solutions methods (PSMs) for solving the Stokes, Oseen, and Brinkman flow problems are presented in this paper. They automatically satisfy the governing equations and are therefore Trefftz-type methods. Utilizing the third-order formulation and three-dimensional analytic functions, we derive a meshless Trefftz-type method to solve three-dimensional Stokes flow problems. The Oseen and Brinkman equations are transformed into four coupled third-order/first-order partial differential equations. The projective-type particular solution (PTPS) is obtained via a projective function in terms of the projective variable; the third-order ordinary differential equations (ODEs) with constant coefficients are derived to determine the projective functions. The Trefftz-type PSM is extremely accurate, because the governing equations (including the incompressibility condition) are implemented automatically. For the Brinkman equations, the general solutions of velocity and pressure are presented by using the Helmholtz function and a harmonic function, whose corresponding Trefftz-type numerical method is developed. Upon comparison with the method of fundamental solutions (MFS), the new methods exhibit some advantages, including lower condition numbers, faster convergence, and better accuracy. We also apply the Trefftz-type PSM to solve the exterior problem of the Stokes equations, where the velocity tends to zero at infinity. Full article

Non-exhaust emissions represent a growing share of traffic-related particulate matter and are increasingly addressed by regulatory frameworks. This study presents a comparison of two brake emission test cycles, the California Brake Dynamometer Cycle (CBDC) and Worldwide Harmonized Light Vehicles Test Procedure Braking Cycle (WLTP-BC), the latter being formally embedded in current regulations. Firstly, we present a detailed comparison of WLTP-BC and CBDC in terms of parameters that are shown to affect or may affect braking control and particle emissions (braking torque, vehicle speed, acceleration, friction work, disc temperature, etc.). Secondly, we present a way to evaluate test system torque control quality, supplementing the friction work-based method present in United Nations Regulation (UNR) No. 179, and quantitatively assess the control quality between the cycles. CBDC was found to be the more challenging cycle to execute. However, the testbench control architecture was found to be sufficient to execute it with high fidelity. Thirdly, we present the emission results obtained from the cycles, both per kilometre driven, as well as per friction work done. We argue that the latter is better for comparing the emission results obtained from cycles with different braking profiles. Driving the CBDC resulted in higher particle mass (PM) emissions but similar particle number (PN) emissions. In light of this dataset, friction work seems to be a better predictor for PN than for PM. While this study encompasses only a single friction pair, and more tests with different brakes would be required to generalize the findings, the results highlight the importance of cycle selection in emission research, both in terms of quantifying the emissions and demands for the test system. Full article

Background: Artificial intelligence (AI) has shown promise in breast ultrasound image analysis, but most evidence still comes from single-dataset studies. Clinical translation requires evaluation under heterogeneous acquisition and curation conditions. This study presents a patient-leakage-aware, reproducible benchmark for breast ultrasound AI under dataset shift, with emphasis on external generalization, calibration, and confidence-related behavior. Methods: A reproducible benchmark framework was developed using patient-level splitting, internal testing, pairwise cross-dataset evaluation, whole-image and region-of-interest (ROI) input strategies, calibration analysis, targeted ROI-margin sensitivity analysis, representative explainable AI visualization, and an auxiliary lesion-versus-normal confidence-based analysis. Four public breast ultrasound datasets (BUSI, BUS-UCLM, BUS-BRA, and BrEaST) were harmonized for a primary benign-versus-malignant lesion classification task. Normal images were excluded from the primary endpoint and used only in auxiliary analyses when sufficient numbers were available. Results: Cross-dataset testing was weaker on average than internal testing, with mean raw AUROC decreasing from 0.801 to 0.719 and mean balanced accuracy from 0.723 to 0.635. ROI input improved external performance, especially for the vision transformer, increasing mean external AUROC from 0.666 to 0.805 and mean external balanced accuracy from 0.594 to 0.713 relative to whole-image input. Temperature scaling improved calibration-related metrics, reducing mean external expected calibration error from 0.180 to 0.150 and mean external negative log-likelihood from 0.848 to 0.682. Conclusions: This study establishes a reproducible benchmark for evaluating breast ultrasound AI under dataset shift, with explicit attention to patient-level leakage control, external validity, and reliability of predicted probabilities. Full article

This paper addresses the problem of determining the underlying structure of a given point process. The point process data is a finite set of event times, given by a set of real numbers. We wish to determine if the process has been generated by one or more periodic processes and, if so, extract the period or periods from the data. If there are several periods, we also wish to deinterleave the data into separate periodic processes, each generated by a single period. We approach the problem by developing two algorithms. These algorithms are designed to work on all data sets, but, in particular, on extremely sparse data sets where other procedures do not work. The first algorithm works on sets of event times with only one underlying period, quickly producing an estimate of that period. The mathematical justification of the procedure involves number theory, including an interpretation of the Riemann zeta function as an asymptotic probability distribution. The second algorithm analyzes event times from multiple periodic processes. It relies on the first algorithm as an “engine” to create larger data sets, from which it produces estimates of underlying periods. This second procedure also relies on a mathematical justification, a result from both number theory and harmonic analysis—the equidistribution theorem of Weyl. We then deinterleave the data, breaking it down into components, each generated by a single period. Full article

An analytical solution is presented for transient heat conduction in a two-layer composite cylinder subjected to outer-surface convection with a general time-dependent ambient temperature. Using Duhamel’s principle, closed-form series expressions are derived and then specialized to harmonic ambient fluctuations, recovering the classical constant-ambient solution in the zero-frequency limit. A parametric study shows that the ratio of the inner layer conductivity to the conductivity of the outer layer strongly shapes interfacial gradients and mean-temperature evolution, with sensitivity concentrated at small ratios and diminishing when the ratio is larger than 0.1. Increasing Biot number accelerates the heat transfer and approaches the isothermal-surface limit as it becomes extremely large. The geometric aspect ratio is most influential when the inner layer is resistive, and becomes weak for large conductivity ratio, supporting thin-coating approximations. Under harmonic ambient fluctuations, the response rapidly reaches a periodic steady state; higher frequency decreases amplitude and increases phase lag, while larger Biot numbers amplify oscillations and reduce delay. The coupled effects of the aspect ratio and the conductivity ratio govern penetration and phase behavior. Full article

This study presents the characterization of the aerodynamic forces and moments acting on irregular particles of prescribed sphericity, generated through truncated spherical harmonic expansions and immersed in a uniform flow at intermediate Reynolds numbers (1 ≤ Re ≤ 200). Particle-resolved direct numerical simulations are conducted using the commercial solver ANSYS Fluent to quantify the statistical behavior of drag, transverse lift, and transverse torque coefficients, along with the corresponding force and moment components, as a function of Reynolds number. Deviations from spherical geometry are shown to induce persistent flow asymmetries, leading to finite transverse lift and torque components even under uniform inflow conditions, effects that cannot be captured by models based on dynamically equivalent spheres. For a sphericity of 0.93, represented by six particle realizations, irregular particles exhibit mean drag values approximately 10% higher than those of spheres with the same equivalent diameter. In addition, both the magnitude and the statistical characteristics of the aerodynamic coefficients are strongly modulated by the combined effects of particle shape irregularity and flow regime. These results provide new insight into the role of geometric complexity in fluid–particle interactions and represent a step forward toward improved predictive capability beyond conventional spherical and quasi-spherical approximations. Furthermore, the present findings provide a physically grounded basis for the development of fluid–particle interaction models for irregular particles, suitable for implementation within Euler–Lagrange simulations of turbulent dispersed flows. Full article

This study presents a comparative Failure Modes and Effects Analysis (FMEA) of electro-hydraulic braking (EHB) and electro-mechanical braking (EMB) systems within brake-by-wire architectures. The analysis integrates both the conventional Risk Priority Number (RPN) approach and the AIAG–VDA Action Priority (AP) methodology, enabling a structured comparison of risk prioritization strategies applied to identical failure modes. A consistent system-level framework is developed to harmonize severity (S), occurrence (O), and detection (D) assessments across both architectures, allowing direct evaluation of methodological differences. The results demonstrate systematic divergences between RPN and AP approaches, particularly in high-severity scenarios, where AP provides more safety-oriented prioritization. The study further identifies key limitations of traditional RPN-based evaluation in safety-critical systems and highlights the advantages of rule-based prioritization frameworks. In addition, corrective measures are proposed and their impact on occurrence and detection ratings is quantified, illustrating practical pathways for risk reduction. Beyond methodological comparison, the work introduces a novel integration of reliability engineering with advanced manufacturing strategies, demonstrating how laser and plasma-based surface engineering can mitigate failure mechanisms by reducing occurrence and improving system robustness. The proposed approach establishes a conceptual and physically grounded bridge between system-level risk assessment and material-level optimization, contributing to the development of more reliable next-generation brake-by-wire systems. Full article

Background/Objectives: Instrument fracture remains a significant complication in endodontics. This study compared the resistance to cyclic fatigue failure between rotary and reciprocating nickel–titanium file systems, as well as differences related to file size and taper. Methods: Nineteen rotary and reciprocating file types (n = 10 per group) were evaluated in three independent test series, harmonized according to file size and system. Cyclic fatigue testing was conducted using a static model with a stainless-steel artificial canal, with an internal diameter of 0.9 mm, a 75° curvature angle, and a fixed radius for each series. Files were operated using preset programs on the X-Smart Plus, Rooter X3000, and Sendoline Endo torque-controlled motors. Time to fracture was recorded digitally, and the total number of full rotations to failure was calculated. The fractured fragments were examined with scanning electron microscopy and fractographic analysis. The data were analyzed using linear models in Stata version 19, with significance set at p ≤ 0.05. Results: Reciprocating file systems demonstrated greater time-to-fracture fatigue resistance than rotary systems. However, these differences were diminished or, in some cases, eliminated when normalized to the number of complete rotations. Fractographic analysis indicated that fractures predominantly resulted from tensile stress rather than shear forces. Conclusions: Reciprocating kinematics generally enhanced fatigue resistance compared with continuous rotation. The results suggest that fatigue resistance in machine-driven nickel–titanium instruments cannot be predicted by motion type or file design alone but reflects a complex interaction between alloy composition, heat treatment, and cross-sectional geometry. Full article

Background/Objectives: Pharmacogenomics (PGx) enables personalized therapy by identifying genetic variants that influence drug response. Despite the advantages of next-generation sequencing (NGS), few clinically validated, guideline-aligned panels comprehensively detect common, rare, and structurally complex pharmacogenetic variants. Methods: We developed and analytically validated Action PharmaKitDx, a targeted NGS panel covering 335 pharmacogenes, including all priority genes recommended by CPIC, DPWG, and CPNDS. Performance was assessed using Coriell HapMap and GeT-RM reference materials across multiple library preparation workflows and Illumina platforms. Clinical feasibility was evaluated in 41 patient samples from diverse specialties. Results were compared with established reference methods, including PCR-based assays, STR analysis, Sanger sequencing, and whole-exome sequencing. Results: Analytical validation: More than 99% of target bases achieved ≥30× coverage. Analytical accuracy, sensitivity, specificity, and positive predictive value exceeded 99.3%, with repeatability and reproducibility >99.7%. Concordance with GeT-RM haplotypes reached 98% after star-allele harmonization. The panel accurately detected complex variants, including CYP2D6 copy-number changes and hybrid alleles. Clinical validation: Full concordance with prior genotyping was observed in clinical samples. Beyond the initial testing indication, each sample harbored a mean of six actionable variants (range 2–10). Thirty-six rare (minor allele frequency <1%) potentially actionable variants were additionally identified. Conclusions: Action PharmaKitDx demonstrates high analytical performance and broad clinical applicability, supporting its implementation as a scalable solution for comprehensive pharmacogenetic testing and precision prescribing. Full article

Active vibration control is crucial for mitigating harmful resonant vibrations in structures subjected to harmonic loads. While antiresonant (zero-placement) methods are effective for this purpose, existing state-feedback solutions require full state measurement, and output-feedback approaches often prioritize resonance assignment over direct harmonic cancellation. This work bridges this gap by proposing a novel systematic design for a proportional–derivative (PD) output-feedback controller to achieve antiresonance for second-order linear systems with a time delay in the actuators. The method first computes a homogeneous gain solution. It then leverages the parametrization of all antiresonant solutions as a constraint within a genetic algorithm optimization. The algorithm optimizes both the stability margin, characterized by an $M_s$-disk criterion, and the number of encirclements of the critical point $(-1,0)$ in the complex plane, as assessed by the Generalized Nyquist Stability Criterion. The proposed approach provides a practical, optimized output-feedback strategy for precise rejection of harmonic disturbances, as demonstrated through a collection of numerical examples from real-world applications. The results confirm the method’s effectiveness in synthesizing stabilizing controllers that enforce antiresonance while ensuring robust stability margins. Full article

High-order Poincaré sphere (HOPS) beams have attracted tremendous interest due to their complex polarization and phase characteristics. However, manipulating the second harmonics generation (SHG) of HOPS beams is still challenging. Here, we developed a vector-coupled wave model to predict petal-shaped intensity patterns and reveal a linear correlation between petal number and topological order (n = 2 → 4). Moreover, we experimentally investigated the multidimensional regulation of SHG in HOPS beams through tailored phase-matching strategies. By employing three distinct configurations—(i) type-I phase matching, (ii) type-II phase matching, and (iii) orthogonally arranged BBO crystals based on Type-I phase matching—we establish a comprehensive framework for controlling the spatial and polarization properties of SHG in n = 2 HOPS beams. These results advance the manipulation of structured light in nonlinear optics, providing insights for optimizing applications in optical communication and polarization imaging. Full article

Dynamic visual cryptography (DVC) can be formulated as a discrete-time reconstruction problem for time-averaged moiré fringes generated by oscillatory transformations of periodic gratings. When implemented on digital display hardware, the continuous oscillatory motion must be realized through discrete frames, which may prevent correct reconstruction of higher-order time-averaged fringes due to refresh-rate limitations. In this work, mathematical criteria are derived to ensure the reliable reconstruction of higher-order time-averaged moiré fringes under finite refresh rate constraints. Harmonic, stochastic, and rectangular temporal waveforms are examined within a unified framework based on the number of frames per oscillation period and the discrete structure of the resulting time-averaged intensity distribution. Stochastic waveforms are shown to not guaranty reproducible fringe formation. For harmonic modulation with a 240 Hz display refresh rate and a 50 Hz oscillation frequency, only four full frames per period are obtained, which is insufficient to reconstruct the third time-averaged moiré fringe requiring at least sixteen frames per period. Rectangular waveforms satisfy the derived reconstruction conditions when the pitch of the grating, the oscillation amplitude, and the resolution of the rendered grating meet explicit constraints. These results establish quantitative parameter bounds for a mathematically consistent software-based DVC implementation on digital displays. Full article

Harmonics and interharmonics have a significant impact on the safe operation of power systems, and accurately identifying interharmonics in power systems is the basis of harmonic suppression. The accuracy with which interharmonic components in power systems are detected is easily affected by mode aliasing and noise; to address this issue, a method of detecting them based on an adjusted Fourier-based synchrosqueezing transform (AFSST) and the three-point symmetric difference energy operator (DEO3S) is proposed. First, in order to reduce the influence of endpoint effects on detection accuracy, an improved waveform feature-matching extension method is utilized to reduce endpoint effects generated during the FSST decomposition process. Then, because it is difficult to adaptively determine the number of ridges in the FSST decomposition process, the energy difference and normalized cross-correlation coefficient are utilized as the criterion for determining the number of modal decompositions in the FSST, thereby improving the accuracy of the ridge number. Finally, using AFSST, the harmonic/interharmonic signals are decomposed into a set of intrinsic mode functions (IMFs). The instantaneous frequency and amplitude of each component are extracted using DEO3S, enabling the accurate detection of harmonics and interharmonics in the power system. Experimental analysis was conducted using simulation data, arc furnace experimental system data, and hardware experimental platform data. The results showed that the proposed method can accurately detect harmonic/interharmonic parameters under different levels of noise interference. Compared with the FSST, EMD, EEMD, and CEEMDAN methods, the amplitude detection accuracy of the proposed method is improved by 0.21%, 0.78%, 0.64%, and 0.75%, respectively, and the amplitude detection accuracy is improved by 1.39%, 3.31%, 2.04%, and 3.14%, respectively. Full article