Search Results (1,050)

This paper presents the design, simulation, and experimental validation of a dual-Circularly Polarized (CP) array antenna to be used as single element for a bistatic radar system, aimed at detecting and tracking objects in Low Earth Orbit (LEO). The antenna operates at 412 MHz in reception mode and consists of an array of 19 slotted-patch radiating elements with a cavity-based metallic superstrate, designed to support dual circular polarization. These elements are arranged in a hexagonal configuration, enabling the array structure to achieve a maximum realized gain of 17 dBi and a Side Lobe Level (SLL) below −17 dB while maintaining high polarization purity. Two identical analog feeding networks enable the precise control of phase and amplitude, allowing the independent reception of Right-Hand and Left-Hand Circularly Polarized (RHCP and LHCP) signals. Full-wave simulations and experimental measurements confirm the high performance and robustness of the system, demonstrating its suitability for integration into large-scale Space Situational Awareness (SSA) sensor networks. Full article

Flavor, as one of the primary factors that attracts consumers, has always been a crucial indicator for evaluating the quality of food. From processing to final consumption, the conditions that affect consumers’ perception of the aroma of aquatic products can be divided into three stages: aroma formation, release, and signal transmission. Currently, there are few reviews on the formation, release, and perception of aroma in aquatic products, which has affected the product development of aquatic products. This review summarizes aroma formation pathways, the effects of processing methods, characteristic volatile compounds, various identification techniques, aroma-release influencing factors, and the aroma perception mechanisms of aquatic products. The Maillard reaction and lipid oxidation are the main pathways for the formation of aromas in aquatic products. The extraction, identification, and quantitative analysis of volatile compounds reveal the odor changes in aquatic products. The composition of aquatic products and oral processing mainly influence the release of odorants. The characteristic odorants perceived from the nasal cavity should be given more attention. Moreover, the relationship between various olfactory receptors (ORs) and the composition of multiple aromatic compounds remains to be understood. It is necessary to clarify the relationship between nasal cavity metabolism and odor perception, reveal the binding and activation mode of ORs and odor molecules, and establish an accurate aroma prediction model. Full article

A series of rivastigmine hybrids, incorporating rivastigmine fragments (RIV) and a set of different antioxidant scaffolds, were designed, synthesized, and evaluated as multifunctional agents for the potential therapy of Alzheimer’s disease (AD). In vitro bioactivity assays indicated that some compounds have very good antioxidant (radical-scavenging) activity. The compounds also displayed good inhibitory activity against cholinesterases, though the bigger-sized hybrids showed higher inhibitory ability for butyrylcholinesterase (BChE) than for acetylcholinesterase (AChE), due to the larger active site cavity of BChE. All the hybrids exhibited an inhibition capacity for self-induced amyloid-β (Aβ_1–42) aggregation. Furthermore, cell assays demonstrated that some compounds showed capacity for rescuing neuroblastoma cells from toxicity induced by reactive oxygen species (ROS). Among these RIV hybrids, the best in vitro multifunctional capacity was found for the caffeic acid derivatives enclosing catechol moieties (4AY5, 4AY6), though the Trolox derivatives (4AY2, 4BY2) presented the best cell neuroprotective activity against oxidative damage. Molecular-docking studies provided structural insights into the binding modes of RIV-based hybrids to the cholinesterases, revealing key interaction patterns despite some lack of correlation with inhibitory potency. Overall, the balanced multifunctional profiles of these hybrids render them potentially promising candidates for treating AD, thus deserving further investigation. Full article

Objective: This cross-sectional content analysis aimed to investigate how oil pulling is portrayed on YouTube Shorts, focusing on the types of speakers, claims made, and alignment with scientific evidence. The study further explored how the content may influence viewer perception, health behaviors, and the potential spread of misinformation. Methods: On 28 January 2025, a systematic search of YouTube Shorts was performed using the term “oil pulling” in incognito mode to reduce algorithmic bias. English language videos with at least 1000 views were included through purposive sampling. A total of 47 Shorts met the inclusion criteria. Data were extracted using a structured coding framework that recorded speaker type (e.g., dentist, hygienist, influencer), engagement metrics, stated benefits, oil type and regimen, the use of disclaimers or citations, and stance toward oil pulling rated on a 5-point Likert scale. Speaker background and nationality were determined through publicly available channel descriptions or linked websites, with user identities anonymized and ethical approval deemed unnecessary due to the use of publicly available content. In total, 47 videos met the inclusion criteria. Results: Of the 47 YouTube Shorts that met the inclusion criteria, most were posted by influencers rather than dental professionals. These videos predominantly encouraged oil pulling, often recommending coconut oil for 10–15 min daily and citing benefits such as reduced halitosis and improved gum health. However, a smaller subset advanced more extreme claims, including reversing cavities and remineralizing enamel. Notably, US-licensed dentists and dental hygienists tended to discourage or express skepticism toward oil pulling, assigning lower Likert scores (1 or 2) to influencers and alternative health practitioners (often 4 or 5). Conclusions: YouTube Shorts largely promote oil pulling through anecdotal and testimonial-driven content, often diverging from evidence-based dental recommendations. The findings reveal a disconnect between professional dental guidance and popular social media narratives. While some benefits like halitosis reduction may have limited support, exaggerated or misleading claims may result in improper oral hygiene practices. Greater engagement from dental professionals and improved health communication strategies are needed to counteract misinformation and reinforce oil pulling’s role, if any, as an adjunct—not a replacement—for standard oral care. Future studies should explore viewer interpretation, behavioral influence, and cross-platform content patterns to better understand the impact of short-form health videos. Full article

CdS nanowires have garnered considerable attention lately for their promising potential in next-generation nanolaser devices, attributed to their relatively high stability and exceptional emission efficiency within the Ⅱ–Ⅵ semiconductor family. In this study, tin-doped CdS nanowires with varying dimensions were synthesized, and the underlying mechanisms responsible for the formation of micro-cavities within these nanowires were systematically explored through scanning electron microscopy (SEM) analysis and photoluminescence mapping. The results show that a very distinct hexagonal-shaped micro-cavity is observed on the cross-section of CdS nanowires, and the size of the micro-cavity is determined by the radius of the nanowire. Additionally, through the use of angle-resolved micro-fluorescence Fourier imaging technology, it is found that under high excitation density conditions, the micro-cavity mode is more prominent at higher collection angles, which is consistent with the mode of the wall-pass cavity micro-cavity. Finally, the formation of the full reflection spectrum of the micro-cavity mode is confirmed through the wavelength shift and intensity shift phenomena related to the excitation power. These results further deepen our understanding of the micro-cavity modes in tin-doped cadmium sulfide nanowires, which may be of great significance for the application of these nanowires in new optical devices. Full article

By measuring the transfer function of the single-mode multi-aperture vertical-cavity surface-emitting laser (SM MA VCSEL) transmitting over a long single-mode fiber at 850 nm, we confirm that the chirp of the SM MA VCSEL under study is dominated by transient chirp with an alpha value of −3.81 enabling a 19 GHz bandwidth over 10 km of single-mode fiber. The detailed measurement of the VCSEL with different bias currents also allows us to recover other key characteristics of the VCSEL, thereby enabling us to practically construct the optical eye diagrams that closely match the experimentally measured ones. The link-level transfer function can be obtained using an analytical equation including effects of modal dispersion and laser chirp–chromatic dispersion (CD) interaction for an MMF of a given length and bandwidth grade. The narrow linewidth and chirp characteristics of the SM MA VCSEL enable transmission performance that surpasses that of conventional MM VCSELs, achieving comparable transmission distances at moderate modal bandwidths for OM3 and OM4 fibers and significantly longer reaches when the modal bandwidth is higher. The transmission performance was also confirmed with the modeled eye diagrams using extracted VCSEL parameters. The chirp properties also provide sufficient bandwidth for SM MA VCSEL transmission over kilometer-scale lengths of single-mode fibers at a high data rate of 100G or above with sufficient optical power coupled into the fibers. Advanced transmission distances are possible over multimode and single-mode fibers versus chirp-free devices. Full article

High-current electron beams can significantly enhance the productivity of variety of applications including medical radioisotope (RI) production and wastewater purification. High-power superconducting radio frequency (SRF) linacs are capable of producing such high-current electron beams due to the key advantage to operate in continuous wave (CW) mode. However, this requires an injector capable of generating electron bunches with high repetition rate and in CW mode, while minimizing beam losses to avoid damage to SRF cavities due to quenching. RF gating to the grid of a thermionic electron gun is a promising solution, as it ensures CW bunch generation at the repetition rate same as the fundamental or sub-harmonics of the accelerating RF frequency, with minimal beam loss. This paper presents detailed beam dynamics simulations demonstrating that an RF-gated gun operating at 1.3 GHz can generate bunches with 148 ps full width with 8.96 pC charge. Full article

As designers push engine efficiency closer to thermodynamic limits, the analysis of flow instabilities developed in a high-pressure turbine (HPT) is crucial to minimizing aerodynamic losses and optimizing secondary air systems. Purge flow, while essential for protecting turbine components from thermal stress, significantly impacts the overall efficiency of the engine and is strictly connected to cavity modes and rim-seal instabilities. This paper presents an experimental investigation of these instabilities in an HPT stage, tested under engine-representative flow conditions in the short-duration turbine rig of the von Karman Institute. As operating conditions significantly influence instability behavior, this study provides valuable insight for future turbine design. Fast-response pressure measurements reveal asynchronous flow instabilities linked to ingress–egress mechanisms, with intensities modulated by the purge rate (PR). The maximum strength is reached at PR = 1.0%, with comparable intensities persisting for higher rates. For lower PRs, the instability diminishes as the cavity becomes unsealed. An analysis based on the cross-power spectral density is applied to quantify the characteristics of the rotating instabilities. The speed of the asynchronous structures exhibits minimal sensitivity to the PR, approximately 65% of the rotor speed. In contrast, the structures’ length scale shows considerable variation, ranging from 11–12 lobes at PR = 1.0% to 14 lobes for PR = 1.74%. The frequency domain analysis reveals a complex modulation of these instabilities and suggests a potential correlation with low-engine-order fluctuations. Full article

In this study, a terahertz microfluidic multi-band sensor was designed. Unlike previous microfluidic absorption sensors that rely on dipole resonance, the proposed sensor uses a physical mechanism for absorption by exciting higher-order lattice resonances in microfluidic structures. With a Fabry–Perot cavity, the sensor can form an absorption peak with a high quality factor (Q) and narrow full width at half maximum (FWHM). A high Q value and a narrow FWHM are valuable in the field of sensing and provide strong support for high-precision sensing. On this basis, the sensing performance of the device was investigated. The simulation results clearly show that the absorption sensor has ultra-high sensitivity, which reaches 400 GHz/Refractive Index Unit (RIU). In addition, the sensor generates three absorption peaks, overcoming the limitations of a single frequency band in a composite resonance mode and multidimensional frequency response, which has potential application value in the field of volatile organic compound (VOC) sensing. Full article

We propose a dual-ring optical filter based on direct binary search inverse design. The proposed device comprises two cascaded rings in an add–drop configuration. A physical model was established using temporal coupled mode theory to derive theoretical spectra and analyze key parameters governing transmission performance. Based on theoretical results, a direct binary search algorithm was implemented. The parameters of the proposed device were calculated using a three-dimensional finite-difference time-domain method for verification. The numerical results demonstrate a free spectral range of 86 nm, with insertion loss and extinction ratios of 0.3 dB and 22 dB, respectively. The proposed device has a narrow spectral linewidth of 0.3 nm within a compact footprint of $24 \mathsf{\mu }\mathrm{m}\times 25.5 \mathsf{\mu }\mathrm{m}$. The device shows significant application potential in laser external cavities and dense wavelength division multiplexing systems. Moreover, this work provides a novel methodology for precision design of photonic devices. Full article

Optically pumped semiconductor disk lasers—known as vertical-external-cavity surface-emitting lasers (VECSELs)—are promising devices for ultrashort pulse formation. For it, a “SESAM-free” approach labeled “self-mode-locking” received considerable attention in the past decade, relying solely on a chip-related nonlinear optical property which can establish adequate pulsing conditions—thereby suggesting a reduced reliance on a semiconductor saturable-absorber mirror (the SESAM) in the cavity. Self-mode-locked (SML) VECSELs with sub-ps pulse durations were reported repeatedly. This motivated investigations on a Kerr-lensing type effect acting as an artificial saturable absorber. So-called Z-scan and ultrafast beam-deflection experiments were conducted to emphasize the role of nonlinear lensing in the chip for pulse formation. Recently, in addition to allowing stable ultrashort pulsed operation, self-starting mode-locked operation gave rise to another emission regime related to frequency comb formation. While amplitude-modulated combs relate to signal peaks in time, providing a so-called pulse train, a frequency-modulated comb is understood to cause quasi continuous-wave output with its sweep of instantaneous frequency over the range of phase-locked modes. With gain-bandwidth-enhanced chips, as well as with an improved understanding of the impacts of dispersion and nonlinear lensing properties and cavity configurations on the device output, an enhanced employment of SML VECSELs is to be expected. Full article

In an optomechanical system (OMS), the dynamics of quantum correlations, e.g., quantum discord, can witness synchronized squeezing between the cavity and mechanical modes. We investigate an OMS driven by two coherent fields, and demonstrate that optimal quantum correlations and squeezing synchronization can be achieved by carefully tuning key parameters: the cavity-laser detunings, loss rates, and the effective coupling ratio between the optomechanical interaction and the amplitude drive. By employing the steady-state solution of the covariance matrix within the Lyapunov framework, we identify the conditions under which squeezing becomes stabilized. Furthermore, we demonstrate that synchronized squeezing of the cavity and mechanical modes can be effectively controlled by tuning the loss ratio between the cavity and mechanical subsystems. Alternatively, in the case where the cavity is driven by a single field, we demonstrate that synchronized squeezing in the conjugate quadratures of the cavity and mechanical modes can still be achieved, provided that the cavity is coupled to a squeezed reservoir. The presence of this engineered reservoir compensates the absent driving field, by injecting directional quantum noise, thereby enabling the emergence of steady-state squeezing correlations between the two modes. A critical aspect of our study reveals how the interplay between dissipative and driven-dispersive squeezing mechanisms governs the system’s bandwidth and robustness against decoherence. Our findings provide a versatile framework for manipulating quantum correlations and squeezing in OMS, with applications in quantum metrology, sensing, and the engineering of nonclassical states. This work advances the understanding of squeezing synchronization and offers new strategies for enhancing quantum-coherent phenomena in dissipative environments. Full article

We demonstrate a novel bidirectional mode-locked ultrafast fiber laser based on an asymmetric dual-cavity architecture that enables freely tunable repetition rate differentials at the kilohertz level, while maintaining inherent common-mode noise suppression through precision thermomechanical stabilization. Through cascaded amplification and nonlinear temporal compression, we obtained bidirectional pulse durations of 33.2 fs (clockwise) and 61.6 fs (counterclockwise), respectively. The developed source demonstrates exceptional capability for asynchronous optical sampling applications, particularly in enabling the compact implementation of real-time measurement systems such as terahertz time-domain spectroscopy (THz-TDS) systems. Full article

Near-unstable cavities hold promise for reducing thermal noise in next-generation gravitational wave detectors and for enhancing light–matter interactions in quantum electrodynamics. However, operating close to the edge of geometrical stability presents significant challenges, including increased coupling to higher-order modes and heightened sensitivity to small cavity length changes and mirror imperfections. This study employs Finesse v3 simulations to systematically investigate the modal behavior of a plano-concave cavity as it approaches instability, incorporating measured mirror surface defects and anisotropic curvature to replicate realistic conditions. The simulations highlight the degradation of beam purity and control signals as the cavity approaches instability. By validating the simulations against experimental data, we confirm Finesse’s reliability for modeling cavities while identifying critical limitations in regimes close to the edge of stability. These findings provide essential guidance for optimizing cavity designs in future gravitational wave detectors, balancing performance gains against the challenges of operating at the stability edge. Full article

The experimental and computational characterization of a cold model prototype designed to test the electromagnetic properties of a new RFQ (Radio-Frequency Quadrupole) cavity is reported. This cavity is intended to be an essential part of a compact, high-gradient proton accelerator for medical purposes. The RFQ’s design employs a novel RF power-coupler injection solution. One common way to couple the RF power in proton RFQs has been the use of loop-couplers inserted into the mid-section of the RFQ’s lobe sections. This technique has been demonstrated to be reliable and effective but introduces a significant perturbation into the lobe that can be more noticeable when dealing with compact structures. We propose a RF injection scheme that uses direct transition from a coaxial cable to the RFQ by connecting the inner coaxial conductor to the RFQ vane body. As a consequence, the lobe geometry is not perturbed, and the transversal electrical fields are directly excited through the vanes. Moreover, by using a pair of such couplers connected to opposite vanes at a given transversal plane of the RFQ, it is also possible to excite the desired quadrupolar TE210 modes while avoiding the excitation of dipolar TE110 modes. The resonances corresponding to different RFQ modes have been characterized, and the dependence of the amplitude of the modes on the relative phase of the field injected through the RF power ports has been demonstrated both by measurements and simulations. Full article