Declining system inertia necessitates quantifying intrinsic frequency support mechanisms. While load voltage dependency influences dynamics, its specific impacts on transient inertial and damping support remain under-quantified. This paper establishes an analytical framework to quantify voltage-dependent load contributions to the initial Rate of Change of Frequency (RoCoF) and frequency nadir. By employing a Center of Inertia (CoI) framework to mathematically isolate load voltage dependence from network oscillations, closed-form expressions are derived for two physical mechanisms. First, the instantaneous power reduction from the subtransient voltage dip functions as an equivalent inertia, proportional to the system’s base mechanical inertia and scaling linearly with grid impedance and load sensitivity. Second, load voltage sensitivity provides an effective damping torque that increases the damping ratio, suppressing the frequency nadir. Furthermore, the study reveals a critical trade-off with Automatic Voltage Regulators (AVR), where aggressive voltage recovery compromises this natural damping support. Time-domain simulations validate that voltage-dependent loads provide a self-regulating defense mechanism, particularly effective in weak grids.
Flight delays impose substantial costs on airlines, airports, and passengers. While existing studies predominantly focus on predicting average delays, extreme delays cause disproportionate operational disruptions and passenger dissatisfaction. This study introduces a distributional sensitivity analysis framework to identify factors that specifically drive extreme flight delays. Using 2.08 million U.S. domestic flights from 2024, we employ quantile regression models combined with Global Distributional Importance and Tangent-SHAP to decompose factor contributions across the entire delay distribution. Our analysis reveals three distinct effect patterns: tail effects, exhibited by weather conditions and carrier service history, which disproportionately amplify extreme delays; location effects, exhibited by realized delay variables such as departure delay and late aircraft delay, which shift the entire distribution approximately uniformly; and center effects, exhibited by flight duration and distance, which primarily affect typical delays. The classification is supported by an extensive robustness suite covering estimator noise, quadrature design, train–test partitioning, and correlation-preserving perturbations. We identify 60 min of departure delay as a critical threshold (bootstrap 95% confidence interval 55–65 min), beyond which 67 percent of flights experience severe arrival delays exceeding 60 min. Summer months exhibit 2.04 times higher tail risk than fall. The estimated annual cost of delays exceeding 60 min is approximately 1.9 billion USD, with potential savings of approximately 1.0 billion USD through targeted interventions. These findings provide actionable insights for airlines and airports to prioritize interventions targeting extreme delay prevention rather than average delay reduction.
Atomically precise copper nanoclusters (Cu NCs) offer a compelling platform for elucidating structure-property relationships in quantum-confined materials, yet isolating ligand-induced electronic effects without altering core geometry remains a fundamental challenge. Herein, we report a systematic study of four compositionally identical Cu11 NCs in which the metal nuclearity and core architecture are strictly preserved, while only the substitution position and electronic nature of the thiolate ligands are varied. By employing methyl- and amino-substituted benzenethiols (ABT) in para and meta configurations, we precisely modulate the ligand-to-metal electronic communication without perturbing the Cu11 architecture. Despite their nearly identical atomic structures, these NCs exhibit strikingly different photoluminescence behaviors. Comprehensive steady-state and time-resolved spectroscopic analyses, complemented by transient absorption measurements and theoretical calculations, reveal that subtle changes in ligand substitution govern excited-state relaxation pathways, long-lived triplet-like excited-state stabilization, and oxygen sensitivity. Among the series, Cu11-3ABT achieves an exceptional photoluminescence quantum yield of 26.1% under inert conditions, arising from effective excited-state stabilization. This work establishes ligand positional engineering as a powerful and general strategy to control emission dynamics in atomically precise Cu NCs, providing fundamental insights into their excited-state physics and offering new design principles for highly emissive, earth-abundant metal NC systems.
Senescence of T cells is strongly linked to organismal aging through two interconnected processes: chronic low-grade inflammation and reduced immune surveillance of senescent cells. T cells are particularly vulnerable to thymic involution, hematopoietic stem cell aging, repeated homeostatic proliferation, chronic antigenic stimulation, and metabolic and mitochondrial dysfunction. As a result, aged T cells may lose their capacity to combat infection and eliminate senescent cells, while also contributing to inflammaging through the production of inflammatory cytokines. Recent preclinical studies in murine models have demonstrated that modulation of T-cell immunosenescence can ameliorate age-related diseases. These approaches include PD-1/PD-L1 blockade, senolytic chimeric antigen receptor T (CAR-T) cells, and CXCL4/platelet factor 4 (PF4). In addition, early-stage human clinical studies of caloric restriction, low-dose mTOR inhibition, thymic regeneration, and mesenchymal stromal/stem cell (MSC) therapy suggest that interventions targeting immunosenescence may provide health benefits. Moreover, in murine models of Alzheimer’s disease, T cells infiltrating the brain may exert either disease-promoting or protective effects depending on the disease stage, highlighting an important point of intersection between T-cell-mediated immunosenescence and brain aging. This review summarizes the basic concepts of immunosenescence, the molecular basis of immune surveillance of senescent cells, age-associated T-cell subsets, their links to brain aging, and interventional strategies aimed at clinical translation, with particular emphasis on T-cell biology and the transcriptional regulatory network driven by NR4a.
YBa₂Cu₃O₇₋δ (YBCO) high-temperature superconductors exhibit enhanced flux pinning capabilities along with high critical temperature (Tc). An improvement in flux pinning and, consequently, the critical current density (Jc) can be achieved by tailoring the precursor phases and their microstructures. In this study, we compare the microstructural modifications of Y₂BaCuO₅ (Y-211) secondary phase particles via ultrasonication processing in de-ionized water (DIW) and ethanol on the superconducting properties of bulk YBCO superconductors.Y-211 precursor powders are engineered by subjecting to high-energy ultrasonication at 450 W for 30 min in de-ionized water and Ethanol. This ultrasonication treatment leads to the formation of nanoscale, surface-modified Y-211 particles, characterized by high surface reactivity and defect density. These pre-treated Y-211 powders are utilized to grow YBCO single grains employing top-seeded infiltration growth (IG) process. Electron microscopy analysis on YBCO bulks revealed a homogeneous microstructure with well-dispersed Y-211 inclusions and embedded sub-phases within the YBCO matrix. Superconducting transition measurements show sharp onset at the temperature of 92 K. The self-field Jc at 77 K enhances to 90 kA/cm² using ultrasonically DIW treated Y-211 powders compared to Ethanol treated (72 kA/cm²) YBCO superconductors. These findings validate the effectiveness of ultrasonically engineered RE₂BaCuO₅ precursors in tailoring flux pinning characteristics and enhancing the performance of REBa₂Cu₃O₇₋δ bulk superconductors.
