Search Results (1,501)

Fast radio bursts (FRBs) are millisecond-duration radio transients of extragalactic origin, while ultra-high-energy cosmic rays (UHECRs; $E\gtrsim {10}^{18}$ eV) remain among the most important unresolved problems in astroparticle physics. This review examines the viability of FRBs and their central engines as sources of UHECRs within a comprehensive multi-messenger framework. We summarize the observational constraints on UHECR source populations imposed by the energy spectrum, nuclear composition, anisotropy measurements, diffuse $\gamma$-ray background, and high-energy neutrino observations, which, together, favor source classes capable of accelerating heavy nuclei with hard injection spectra, modest cosmological evolution, and sufficiently high source densities. We then review the current landscape of FRB progenitor and engine models, including magnetars, supramassive neutron stars, compact-object mergers, and accretion-powered systems, emphasizing their energetics, environments, and particle-acceleration capabilities through relativistic shocks, magnetic reconnection, magnetar wind nebulae, and direct electromagnetic acceleration by ultra-relativistic FRB pulses. We discuss how these scenarios are constrained by neutrino and $\gamma$-ray observations from IceCube, KM3NeT, and Fermi-LAT, as well as by large-scale UHECR anisotropy measurements from the Pierre Auger Observatory and Telescope Array. Finally, we examine the observational tests that will become possible in the coming decade through large samples of localized FRBs, composition-resolved UHECR measurements, next-generation neutrino observatories, and wide-field $\gamma$-ray facilities. We emphasize that FRB dispersion and rotation measures provide unique probes of the baryonic and magnetic environments relevant for UHECR acceleration and propagation, enabling a new form of multi-messenger tomography of cosmic-ray source environments and allowing the FRB–UHECR connection to become a quantitatively testable astrophysical framework. Full article

Surface-enhanced Raman scattering (SERS) offers a powerful route for biomolecular detection because it combines molecular specificity with high sensitivity, rapid optical readout, and multiplexing capability. In real biological samples, however, analytical performance is rarely determined by signal enhancement alone. Biofluids such as serum, plasma, saliva, urine, and interstitial fluid contain complex biomolecular mixtures that interfere with target capture, spectral response, and data interpretation. A practical SERS biosensor must therefore localize targets, stabilize spectral responses, tolerate matrix-induced variation, and convert complex spectra into reliable analytical information. This review discusses recent progress in SERS biosensing from an integrated system perspective, with particular focus on artificial intelligence/machine learning (AI/ML)-assisted interpretation. Direct label-free SERS provides chemically transparent readouts but is limited by stochastic adsorption, hotspot heterogeneity, and spectral variation in complex samples. Bio-recognition interfaces improve target localization, while signal-transduction strategies based on nanotags, immunoassays, clustered regularly interspaced short palindromic repeats (CRISPR) systems, nanozymes, and lateral-flow formats decouple molecular recognition from spectral generation. Digital SERS further improves measurement robustness by converting fluctuating intensities into countable, event-based outputs. AI/ML-assisted analysis can support full-spectrum classification, calibration transfer, explainability, and patient-level decision-making. We frame AI/ML-assisted SERS biosensing as an integrated architecture connecting substrate design, interface engineering, signal transduction, digital measurement, and clinical validation. Future progress will depend as much on validation-ready workflows as on plasmonic enhancement itself, especially for systems intended to operate across different samples, instruments, and clinical settings. Full article

Based on the analysis of the emission spectra of LiNbO₃:Ho³⁺ and LiNbO₃:Yb³⁺ crystals in the infrared region, the feasibility of radiation-balanced (RB) lasing in the infrared region at room temperature has been investigated. The parameters of RB lasing were calculated, and the optimal pump and laser wavelengths were determined as follows: λ_OP = 2015.2 nm and λ_OL = 2072.3 nm for LiNbO₃:Ho³⁺ crystals, and λ_OP = 1004.7 nm and λ_OL = 1060.8 nm for LiNbO₃:Yb³⁺ crystals. The dependence of RB lasing intensity on pump intensity, ensuring radiation balance, was established. For representative values of intracavity losses (γ_i = 0.1%, 0.4%, 0.8%) and output coupler transmission losses (T₂ = 2%), the expected output powers of RB lasing were estimated. Full article

Reconfigurable photonic metasurfaces enable tunable thermal-emission engineering in the long-wave infrared (LWIR), particularly within the 8–13 μm atmospheric window. This work includes the investigation on a concentric-ring VO₂/SiO₂/Au metasurface for LWIR spectral-emissivity modulation. Full-wave simulations showed that, in the metallic phase (σ = 2 × 10⁵ S/m where σ is conductivity), the structure exhibited an absorption over 90% across the 9.3–15 μm sub-band, with two near-unity resonances near 10.2 and 13.3 μm. Control structures, gap-dependent spectra, E-field maps, and current-density Cartesian multipole decomposition supported a hybridized-ring mechanism in which both dominant resonances were predominantly electric-dipole-like ring branches whose spectral positions and field localizations were modified by inter-ring coupling. Across the conductivity sweep, the normal-incidence band-averaged 8–13 μm emissivity changed from 0.0184 to 0.8844, corresponding to a switching ratio of 48.06. The four-fold symmetry of unit cell also yielded polarization-insensitive and angularly robust LWIR absorption, while the simplified endpoint thermal-balance estimate indicated a metallic-state net cooling power of 49.3 W m⁻² at T = T_amb = 300 K, where T_amb was the ambient temperature, and an estimated equilibrium temperature drop of 4.4 K below the ambient for the metallic-state endpoint, whereas the insulating-state one suppressed this response. These results identify concentric VO₂ ring metasurfaces as promising candidates for switchable LWIR thermal-emission control. Full article

L-carnitine plays a central role in mitochondrial fatty acid transport and cellular energy regulation; effects on the biochemical phenotype of brain cancer cells remain insufficiently characterized. Here, we applied confocal Raman spectroscopy and imaging to investigate the biochemical alterations induced by L-carnitine supplementation—administered as its tartrate salt—in human astrocytoma cells. Raman spectral analysis revealed distinct changes in lipid-, protein-, nucleic acid-, and cytochrome-associated vibrational features following 24 h of treatment, suggesting alterations in mitochondrial activity and cellular energy-related processes. Principal component analysis identified PC1 (93.87%) as representing the intrinsic biochemical composition of the cells, whereas PC2 (1.19%) and PC3 (0.59%) captured subtle yet consistent variations in lipid organization, protein conformation, and redox-sensitive vibrational features associated with L-carnitine exposure. Pearson correlation analysis of Raman cluster spectra indicated biochemical differences across cellular compartments, with the most pronounced changes observed in lipid droplets, supporting modifications in lipid-associated cellular processes. These findings demonstrate that Raman imaging provides a sensitive, label-free platform for resolving L-carnitine-induced biochemical heterogeneity at the single-cell level. Overall, this study highlights vibrational spectroscopy as a powerful tool for characterizing cellular responses to metabolic modulators and provides insight into the biochemical impact of exogenous L-carnitine in brain cancer cells. Full article

Aging disrupts sleep, but how these changes are structured across circadian time, vigilance states, and sex remains poorly understood, because most prior studies used single-sex cohorts and few days of recordings. We continuously recorded 14 days of EEG/EMG in 24 C57BL/6J mice using a balanced 2 × 2 design (young vs. old; male vs. female; n = 6/group). A comprehensive multiscale analysis of the extended dataset enabled detailed reconstruction of 24 h sleep–wake architecture, better characterization of natural day-to-day variability including across multiple estrous cycles, and detection of rare bouts and transition events. Across seven levels of analysis, from circadian profiles to EEG spectral parameterization, the strongest aging effect was a dark-phase-specific 17–18% loss of theta-dominant active wake (TDW) in both sexes, with reciprocal increases in quiet wake (nTDW) and NREM sleep. We also identified a recurring N-shaped structural motif at the dark-to-light transition, where age-related and several sex-associated differences were most apparent. Broadly, old mice exhibited (i) shorter TDW bouts; (ii) a shift in NREM exit kinetics toward wakefulness; (iii) more brief and poorly consolidated “out-block” NREM episodes; and (iv) a slowing of waking theta and higher low-frequency TDW power. Variance decomposition indicated that statistical power depends more on sample size than on recording length. Together, aging reflects a coordinated, circadian-phase-specific reorganization of sleep–wake architecture. Sex-related and interaction findings should be interpreted as hypothesis-generating pending larger cohorts. Full article

Low-temperature photoluminescence (PL) has been studied under hydrostatic pressure and varying excitation powers in three samples of single In_0.17Ga_0.83N quantum wells with different widths: 2.6 nm, 5.2 nm, and 10.4 nm. Transitions involving ground states were strong in the 2.6 nm well, weak in the 5.2 nm well, and absent in the 10.4 nm well. Pressure coefficients of PL lines have been used to estimate the electric field in the wells. In the widest well, the field seems to be fully screened (at high excitation powers). Simulations involving Poisson and Schrödinger equations allowed us to identify the experimental PL lines. Pressure evolution of the PL spectra agreed with the simulation. We present diagrams showing the dependence of the field in the well on pressure and on carrier concentration. In wide wells, these diagrams illustrate the transition from a 2D-like system to a 3D-like system. Full article

Solar cell efficiency depends on both photogeneration and charge collection, with the active layer playing a key role in these processes. In organic solar cells (OSCs), where power conversion efficiency (PCE) remains relatively low, understanding the influence of active layer and metal contact thickness on device performance is essential. In this work, we investigate the effect of P3HT:PCBM and Ag thickness on OSC performance by analyzing the evolution of electrical parameters obtained from J-V measurements over five weeks, with particular attention given to resistance-related degradation behavior. The analyzed OSCs had a cell structure composed of Ag/P3HT:PCBM/TiO₂/ITO/glass, and each material was corroborated by XRD and Raman spectroscopy. The thickness of P3HT:PCBM was modulated by varying the number of spin-coated layers from 1 to 3 (ranging from 75 to 160 nm). This variation increases light absorption, as demonstrated by the optical transmittance spectra. However, device degradation became evident after the third week of fabrication, mainly due to an increase in series resistance, which adversely affected the open-circuit voltage (V_OC), fill factor (FF), and overall device efficiency. The best performance was obtained for devices fabricated with two P3HT:PCBM layers and 18 mg of Ag, achieving a maximum PCE of 0.5%. Full article

Hereditary damping and fractional attenuation are widely used to model wave propagation in complex media, but the variational and spectral origin of the corresponding nonlocal-in-time operators is often left implicit. In this work, we derive such operators from a minimal conservative field–reservoir model. A real scalar field is coupled locally to a continuum of harmonic reservoir modes, which are then eliminated exactly. The resulting reduced dynamics is a causal wave equation with a memory-friction term acting on the field velocity. The memory kernel is generated by the reservoir coupling spectrum through a cosine-transform relation, establishing a direct spectrum-to-kernel correspondence. This relation provides both a physical interpretation of hereditary damping and a practical admissibility criterion: macroscopic attenuation and dispersion arise from the delayed back-action of unresolved internal modes, while physically admissible kernels are constrained by the non-negativity of the underlying spectral density. The framework unifies several standard damping regimes. A broadband reservoir recovers the Markovian locally damped wave equation, reservoirs with a finite characteristic time generate finite-memory relaxation and frequency-dependent dispersion, and scale-free reservoir spectra produce power-law memory kernels. In the latter case, the hereditary damping operator reduces to a Caputo-type fractional derivative, showing that fractional wave attenuation can emerge as an effective reduced dynamics rather than being postulated phenomenologically. We further analyze dispersion, attenuation, causality, stability, and admissibility conditions in terms of the reservoir spectrum. The main contribution of the work is therefore to provide a variational and spectral derivation of hereditary and fractional wave damping, linking the structure of unresolved reservoir modes to macroscopic nonlocal wave dynamics. Full article

The detection and quantification of reactive oxygen and nitrogen species (RONS) in plasma-treated water (PTW) are essential for advancing plasma applications in biomedical and agricultural fields. However, RONS characterization remains challenging, as conventional techniques often require chemical reagents that can alter the sample. Electrochemical impedance spectroscopy (EIS) offers a non-destructive alternative by probing the electrical response of aqueous systems and providing information on ionic concentration, charge transfer, and diffusion processes. This study investigates the feasibility of EIS as a diagnostic tool for characterizing physicochemical changes in PTW. Calibration experiments were performed using saline solutions with different ionic concentrations to evaluate the sensitivity of impedance measurements. Impedance spectra were recorded over a frequency range of 0.1 Hz to 10 kHz and analyzed using Nyquist and Bode plots with equivalent circuit modeling. Deionized water was treated with cold atmospheric plasma at different discharge powers (3.53–10.15 W) and treatment times (5–30 min) to generate RONS. The results show that EIS can monitor plasma-induced changes in conductivity and interfacial properties associated with variations in ionic content. In particular, systematic changes in solution resistance and admittance were observed and were correlated with plasma-induced changes in ionic composition. These findings demonstrate that EIS is a sensitive and non-invasive diagnostic method for PTW analysis. Full article

Background: This study analyzed spectral alterations of heart rate variability (HRV) in Williams syndrome (WS) during sleep, taking into account the multi-fractal properties of RR-interval spectra, including effects of aging and sleep structure. Methods: Using ECG recordings of 20 subjects with WS and matched typically developing (TD) controls, fractal and oscillatory spectral components of RR-intervals were computed. The fractal component was parametrized with a piecewise-linear function, allowing a breakpoint and separate slope and intercept values in the lower- and higher-frequency domains. The dominant peak frequency and prominence were extracted from the LF (0.04–0.15 Hz) and HF (0.15–0.4 Hz) bands. Results: Strong WS/TD group differences were found in the breakpoint frequency, high domain slope, intercept and HF peak prominence. The LF peak frequency showed a slight age-dependent decrease only in TD, and reduced values in WS independent of age. Principal component analysis identified a main fractal component describing typical alterations in the spectrum in WS, which exhibited sleep-structure associations. Conclusions: The broken power-law model successfully characterized the fractal component of RR-interval spectra, capturing altered cardiac regulation in WS, while suggesting the fractal parameters as possible biomarkers of the degree of general autonomic deregulation. Full article

We investigatewhether a finite local information capacity of spacetime can account for the gravitational phenomena commonly attributed to cold dark matter. Starting from a covariant effective-field-theory description, we modelcoarse-grained entropy deposition as a dynamical scalar field $S\left(x\right)$ whose stress–energy tensor contributes to structure formation. The macroscopic action contains a single dimensionless coupling λ multiplying the canonical kinetic term, ensuring ghost-free dynamics and conservation of the associated stress–energy tensor. In a slow-roll regime, defined by a covariant source term $\Gamma \equiv \ddot{S}+3H\dot{S}=0$, where H is the Hubble parameter and overdot denotes derivative with respect to cosmic time, and $|\ddot{S}|\ll H|\dot{S}|$, the entropy sector behaves as pressureless dust at background and in linear order. Implemented in a modified Cosmic Linear Anisotropy Solving System (CLASS) Boltzmann solver, the entropy component fits Planck satellite 2018 cosmic microwave background (CMB) data, baryon acoustic oscillation (BAO) measurements, and the Pantheon + Type Ia supernova sample for $0.5\lesssim \lambda \lesssim 2$, while preserving the linear growth factor to within 0.2% over Euclid space telescope scales. To regulate ultraviolet contributions, we introduce a holographically motivated prescription in which gravitationally active entropy deposition is confined to causal two-surfaces, yielding a $\rho \propto r^{-2}$ halo envelope with a finite-density core determined by local entropy saturation. Fixing the flux scale $\mathcal{A}$ from astrophysical entropy budgets reproduces Milky-Way-mass halos without introducing fine-tuned length scales. Pilot N-body simulations that evolve the entropy field on a staggered grid reproduce the halo mass function down to ${10}^{10.5}{M}_{\odot }$, mitigate the cusp–core and missing-satellite tensions, and remain consistent with cluster lensing constraints. On linear scales, the model predicts percent-level, scale-dependent deviations in the lensing convergence and matter power spectra, testable by Euclid space telescope, the Roman Space Telescope High Latitude Survey, and the CMB-S4 experiment. Full article

Carbon dots (CDs) are emerging nanomaterials with promising applications in food science. Recent reports have shown that carbon dots are inherently present in heat-treated foods and beverages. However, the occurrence of carbon dots in traditional Korean beverages has not yet been investigated. In this study, carbon dots were isolated from three Korean beverages, Nurungji tea, barley tea, and green tea, and characterized using TEM, DLS, ζ-potential, UV-absorbance, photoluminescence (PL), FTIR and XPS analyses. All three beverages contained quasi-spherical (<10 nm) CDs, consistent with quantum dots whose optical properties depend on their size. DLS and ζ-potential measurements (−40 mV for cereal tea and −14 mV for green tea) confirmed their colloidal stability without aggregation in the beverages. PL spectroscopy exhibited excitation-dependent emission with a bathochromic shift, peaking at 412–438 nm, and FTIR spectra revealed abundant O-H, N-H, C=O, and C-N functional groups, reflecting oxygen and nitrogen doping that modulate redox reactions. Due to these surface functional groups, CDs demonstrated excellent antioxidant activity, with green tea CDs achieving 100% scavenging activity at 12.5 µg/mL, while barley and Nurungji CDs reached 100% and 78% scavenging activities at 100 µg/mL, respectively. In the cytotoxicity test using L929 fibroblast cells, grain tea CDs showed a survival rate of over 90% at concentrations of 6.25–100 µg/mL, and green tea CDs showed a survival rate of over 90% at concentrations up to 25 µg/mL, which is consistent with the literature on the biocompatibility of CDs. These results confirm that beverage-derived CDs are non-toxic and powerful antioxidants, reaffirming the safety and functionality of traditional Korean food. Full article

Gallium oxide is an ultra-wide bandgap semiconductor with excellent opto-electronic properties, making it a highly promising material for a wide range of applications and devices. In this article, we report how the optical, morphological, structural, and compositional properties of $\beta$-Ga₂O₃ thin films deposited by RF Sputtering on silicon substrates are affected by thermal treatments. Ellipsometric spectra recorded at multiple angles of incidence from several samples subjected to thermal annealing in the range of 550–1000 °C were analyzed to extract the optical functions using appropriate multilayer models. This analysis is complemented by compositional, structural, and morphological characterization techniques. We observed two main stages of crystallization with increasing annealing temperature; up to 700 °C, there is an increase in density and then, for 700–1000 °C, there is an improvement in crystallinity. While the refractive index increases continuously throughout this process, we found that the polarizability of the samples decreases in the first stage and increases in the second. These observations demonstrate that thermal treatments are a powerful tool to tune the optical properties of Ga₂O₃ thin films for device applications. Full article

Quark–gluon dynamics within protons and high-energy radiation phenomena in the universe are typically regarded as two entirely distinct fields. This paper aims to demonstrate that gluon condensation (GC) may serve as a direct bridge between these two fields. We review three key aspects of GC research: first, the Zhu–Shen–Ruan (ZSR) equation, as a nonlinear evolution equation based on structural symmetry, exhibits self-consistent connections with the DGLAP, BFKL and GLR-MQ-ZRS equations, providing a theoretical foundation for the generation of GC; second, the chaotic solutions and the shadowing–antishadowing synergy inherent in this equation can drive gluons to aggregate near the critical momentum, thereby forming a novel type of high-density, strongly interacting matter; third, these changes in microstructure manifest themselves as a broken-power-law feature in high-energy cosmic gamma-ray spectra, thereby offering new insights into the hadronic scenarios underlying certain astrophysical sources. Consequently, GC not only concerns the novel behaviour of quantum chromodynamics under extreme conditions but may also serve as a vital window for probing the deep structure of protons using cosmic-ray signals. With the advancement of higher-precision gamma-ray observations, hadron collision experiments and related theoretical research, the physical picture of GC and its observational criteria are expected to undergo more rigorous testing. Should this picture be confirmed, certain features in the high-energy gamma-ray spectrum (previously attributed solely to empirical fitting or lepton models) will need to be re-examined within the deeper context of hadronic dynamics; simultaneously, GC may also provide a new entry point for research into pion condensation in nuclear physics and even condensed matter physics. Consequently, the significance of the search for GC extends beyond the model itself, reaching into multiple fields of natural science. Full article