Search Results (17)

Ice lenses in natural frozen soils commonly exhibit inclined and heterogeneous distributions, and their spatial morphology significantly influences the mechanical behavior of frozen soils. To investigate the coupled regulatory mechanism of ice lens inclination angle and thickness on the mechanical properties of frozen silty clay, specimens containing artificial single-layer ice lenses with varying inclination angles (0°, 10°, 20°, 30°) and thicknesses (5 mm, 15 mm) were prepared under constant temperature, water content, and loading rate conditions. Low-temperature uniaxial compression tests were conducted, and the results were systematically analyzed in conjunction with discrete element method (DEM) simulations and a modified Duncan–Chang model. The results indicate that increasing the ice lens inclination angle leads to a nonlinear reduction in the deviatoric stress at 15% axial strain, with the failure mode transitioning from compression-induced bulging to shear sliding dominance. When the ice lens thickness increased from 5 mm to 15 mm, the deviatoric stress at 15% axial strain further decreased across all inclination angles, accompanied by a reduction in the composite modulus. The response surface prediction formulas for parameters a and b, established based on experimental data, effectively describe the stress–strain relationships. DEM simulations reveal, at the mesoscale, the asymmetric displacement field and shear band evolution mechanisms governed by inclined ice layers, with bond breakage accelerating as the inclination angle increases. This study clarifies the coupled effects of ice lens spatial configuration and confining pressure on the mechanical response of frozen soils, providing a theoretical reference for bearing capacity assessment of frozen ground containing inclined ice lenses. Full article

How does artificial intelligence (AI) adoption shape administrative efficiency and e-citizen integration in local governments, and what role does professional development play in mediating these relationships? Drawing on a survey of 500 municipal employees across Spanish municipalities, this study employs partial least squares structural equation modelling (PLS-SEM), with formal non-linearity testing via Warp3 algorithms, to test a theoretically grounded model. The conceptual framework integrates Digital Transformation Theory and Public Value Theory as primary explanatory lenses, while drawing on the Technology Acceptance Model (TAM) and Total Factor Productivity (TFP) logic as complementary background perspectives that contextualise rather than directly operationalise the micro-level findings. Structural results reveal that AI adoption exerts a strong direct (and statistically linear) effect on perceived administrative efficiency (β = 1.04, p < 0.001; the standardised coefficient exceeding 1.0 and R² > 1 are a legitimate WarpPLS warp-model fit index rather than evidence of model misspecification: the Warp3 warp functions inflate the variance of predicted efficiency and break the additive identity SST = SSM + SSE, with the high AI–PD collinearity (r ≈ 0.84) as the contributing mechanism (RSCR = 1.000, SSR = 1.000); a comparative re-estimation without the moderation term yields β = 0.87 and R² = 0.76; we adopt this parsimonious specification (β ≈ 0.87, R² = 0.76) as the substantively interpretable estimate, with predictive relevance confirmed by a high Stone–Geisser Q² = 0.685, indicating that the model fits and predicts well rather than overfitting, while simultaneously stimulating professional development (β = 0.84, p < 0.001, R² = 0.70). Professional development positively predicted both efficiency (β = 0.27, p < 0.001) and e-citizen integration (β = 0.26, p < 0.01). Efficiency is the primary driver of e-citizen integration (β = 0.54, p < 0.001, R² = 0.53). The proposed moderation of AI adoption by professional development on efficiency was not supported (β = −0.01, p = 0.44), suggesting additive rather than synergistic effects. Model fit was robust (GoF = 0.701; ARS = 0.749; APC = 0.495); convergent and discriminant validity were confirmed by composite reliability, average variance extracted, Fornell–Larcker, and HTMT criteria; and common method bias diagnostics (Harman’s single-factor test, full-collinearity AFVIF, and marker-variable analysis) indicated that systematic method variance was not a material threat. These findings offer micro-empirical evidence of the mechanisms linking AI adoption to citizen service outcomes via a professional development pathway and provide actionable recommendations for Spanish and European municipalities navigating AI-driven governance reform. Full article

We consider a model problem of polarization-dependent light bending and time delays in the vicinity of neutron stars endowed with magnetar-strength magnetic fields (B∼${10}^{15}\mathrm{G}$), combining an effective-metric formulation of Heisenberg–Euler nonlinear electrodynamics with general-relativistic ray tracing. The spacetime geometry is analyzed using both the Kerr metric and a quadrupole-deformed q-metric, characterized by a quadrupole parameter varying in the range $q\in [{10}^{-3},0.5]$. In addition, the impact of complex magnetic-field topologies is examined by introducing a magnetic quadrupole component alongside the dipole configuration. The simulations performed in this study demonstrate that the inclusion of the quadrupole deformation parameter significantly modifies photon trajectory deflections compared to the standard Kerr solution. We further quantify the geometric dilution of the photon beam, finding a cross-section expansion ratio of approximately $4.7\times {10}^{13}$ for rays reaching Earth. This strong dilution imposes stringent constraints on the detectability of polarization-dependent signatures and time-delay echoes. Finally, characteristic illustrations are presented for trajectory distortions, bending-angle distributions, and intensity valleys produced by the combined gravitational and magnetic lensing effects. Full article

A general relativistic model of an astrophysical hypermassive extremely magnetized ultra-compact self-bound quark–gluon plasma (QGP: ALICE/LHC) object that is supported against its ultimate gravitational implosion by the simultaneous action of the vacuum polarization driven by nonlinear electrodynamics (NLED: ATLAS/LHC: light-by-light scattering)—the vacuum “awakening”—and the asymptotic freedom, a key feature of quantum chromodynamics (QCD), is presented. These QCD stars can be the final figures of the equilibrium of collapsing stellar cores permeated by magnetic fields with strengths well beyond the Schwinger threshold due to being self-bound, and for which post-supernova fallback material pushes the nascent remnant beyond its stability, forcing it to collapse into a hybrid hypermassive neutron star (HHMNS). Hypercritical accretion can drive its innermost core to spontaneously break away color confinement, powering a first-order hadron-to-quark phase transition to a sea of ever-freer quarks and gluons. This core is hydro-stabilized by the steady, endlessly compression-admitting asymptotic freedom state, possibly via gluon-mediated enduring exchange of color charge among bound states, e.g., the odderon: a glueball state of three gluons, or either quark-pairing (color superconductivity) or tetraquark/pentaquark states (LHCb Coll.). This fast—at the QGP speed of sound—but incremental quark–gluon deconfinement unbinds the HHMNS’s baryons so catastrophically that transforms it, turning it inside-out, into a neat self-bound QGP star. A solution to the nonlinear Tolman–Oppenheimer–Volkoff (TOV) equation is obtained—that clarifies the nonlinear effects of both NLED and QCD on the compact object’s structure—which clearly indicates the occurrence of hypermassive QGP/QCD stars with a wide mass spectrum ($0\lesssim {\mathrm{M}}_{\mathrm{Star}}^{\mathrm{QGP}}\lesssim$ 7 M_⊙ and beyond), for star radii ($0\lesssim R_{\mathrm{Star}}^{\mathrm{QGP}}\lesssim 24$ km and beyond) with B-fields (${10}^{14}\le {\mathrm{B}}_{\mathrm{Star}}^{\mathrm{QGP}}\le {10}^{16}$ G and beyond). This unexpected feature is described by a novel mass vs. radius relation derived within this scenario. Hence, endowed with these physical and astrophysical characteristics, such QCD stars can definitively emulate what the true (theoretical) black holes are supposed to gravitationally do in most astrophysical settings. This color quark star could be found through a search for its eternal “yo-yo” state gravitational-wave emission, or via lensing phenomena like a gravitational rainbow (quantum mechanics and gravity interaction), as in this scenario, it is expected that the light deflection angle—directly influenced by the larger effective mass/radius (${\mathrm{M}}_{\mathrm{Star}}^{\mathrm{QGP}}\left(B\right)$, ${\mathrm{R}}_{\mathrm{Star}}^{\mathrm{QGP}}\left(B\right)$) and magnetic field of the deflecting object—increases as the incidence angle decreases, in view of the lower values of the impact parameter. The gigantic—but not infinite—surface gravitational redshift, due to NLED photon acceleration, makes the object appear dark. 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

The research on high-order transverse modes in lasers was largely abandoned a few years after the invention of the laser in 1960. The main reason for this was that high-order beams are more divergent and less bright than the Gaussian beam. In the present paper, we showed that the behaviour of $L{G}_{p0}$ beams faced to the optical Kerr effect (OKE) varies considerably depending on the mode order (p = 0 or $p\ge 1$). We focused our attention on the properties of $L{G}_{00}$ and $L{G}_{10}$ beams when subject to OKE, and we found that the $L{G}_{10}$ beam keeps its focusability much better than the $L{G}_{00}$ beam. This property has at least two applications concerning first the conception of high-intensity laser chains not based on a Gaussian beam but on an $L{G}_{10}$ beam and second, the use of an $L{G}_{10}$ beam instead of the usual Gaussian beam which can reduce drastically the protection of optical limiters based on OKE; this constitutes a counter-measure against such limiters. Full article

This paper explores the optical approach to simplifying complex concepts in general relativity (GR) and nonlinear vacuum electrodynamics. The focus is on using optical analogies to simplify the understanding of spacetime curvature and interactions in strong gravitational and magnetic fields. We demonstrate how applying concepts of effective refractive index can facilitate the teaching and comprehension of GR optical effects, such as gravitational lensing and the behavior of light around massive objects. Additionally, the paper covers the application of optical analogies in the context of nonlinear vacuum electrodynamics, showing how strong magnetic fields affect light propagation. This interdisciplinary approach provides a more natural understanding and modeling of complex physical phenomena, making them better accessible for study and teaching. Full article

Ytterbium laser sources are state-of-the-art systems that are increasingly replacing Ti:Sapphire lasers in most applications requiring high repetition rate pulse trains. However, extending these laser sources to THz Time-Domain Spectroscopy (THz-TDS) poses several challenges not encountered in conventional, lower-power systems. These challenges include pump rejection, thermal lensing in nonlinear media, and pulse durations exceeding 100 fs, which consequently limit the detection bandwidth in TDS applications. In this article, we describe our design of a THz-TDS beamline that seeks to address these issues. We report on the effectiveness of temperature controlling the Gallium Phosphide (GaP) used to generate the THz radiation and its impact on increasing the generation efficiency and aiding pump rejection while avoiding thermal distortions of the residual pump laser beam. We detail our approach to pump rejection, which can be implemented with off-the-shelf products and minimal customization. Finally, we describe our solution based on a commercial optical parametric amplifier to obtain a temporally compressed probe pulse of 55 fs duration. Our study will prove useful to the increasing number of laboratories seeking to move from the high-energy, low-power THz time-domain spectroscopy systems based on Ti:Sapphire lasers, to medium-energy, high-power systems driven by Yb-doped lasers. Full article

Presbyopia correction through implantation of a trifocal intraocular lens (IOL) is a modality offered to both cataract and refractive-lens exchange patients. To maximize postoperative satisfaction, IOL selection needs to be made based on patients’ requirements aligned with the available technology. Five Trifocal IOLs were assessed in this study, and their differentiating features were identified: Triumf POD L GF, AT Lisa Tri, Tecnis Synergy, AcrySof IQ PanOptix, and Acriva Trinova Pro C. The optical quality was assessed using the modulation-transfer-function principle. Simulated defocus curves were derived from a non-linear formula. Far-focus simulated visual acuity (simVA) was 0.03 logMAR or better for all the studied IOLs, showing minimal differences. However, each IOL’s intermediate focus position differed across a range from 61 cm to 80 cm; and for the near focus, it was 36 cm to 44 cm. Triumf demonstrated improved intermediate point at the expense of the near focus resulting in a lower predicted near VA. PanOptix exhibited the shortest range of vision without a clear distinction between intermediate and near-point. The remaining lenses presented three foci of comparable optical quality and, thus, simVA performance. Each model, however, revealed a different aperture-change response. Trinova function improved at intermediate but was worse at near for larger pupils. The opposite was observed for AT Lisa. Synergy’s optical quality change was predominantly associated with lower pupil diameter. In conclusion, the trifocal IOLs can be differentiated according to their secondary-foci position, light-energy distribution, and pupil-size-related behavior. The observed differences may translate directly into a clinical effect showing that the trifocal IOLs vary in their ability to deliver optimal vision at different distances, with some providing improved intermediate while others favor reading distance. The knowledge gained through this objective testing can support IOL selection, postoperative patient counselling and increase the chance of spectacle independence after surgery. Full article

Hyperbolic metamaterials (HMMs) exhibit high tunability in photonic devices. This study numerically investigates light propagation in photonic crystal (PhC) membranes containing HMMs. The proposed HMM PhC membranes contain square HMM rods, which comprise dielectric (Si) and metallic (Ag) layers. Owing to their property of subwavelength field localization, HMMs can be applied to PhCs to improve tunability and thus enhance the self-collimation (SC) effect of PhCs. The SC points were obtained in the second HMM PhC band, wherein the nearby dispersion curves change significantly. In addition, the effect of the HMM filling factor (i.e., the ratio of the metal-layer to unit-cell thicknesses) on the SC point frequency is studied. Finally, we demonstrate the efficient control of beam behaviors using HMM PhC membranes while considering the nonlinearity of Ag. The findings of this study confirm that high-performance HMM PhC membranes can be employed in nonlinear all-optical switches, filters, tunable lenses, and other integrated optical devices. Full article

The aim of manufacturing can be described as achieving the predefined high quality product in a short delivery time and at a competitive cost. However, it is unfortunately quite challenging and often difficult to ensure that certain quality characteristics of the products are met following the contemporary manufacturing paradigm, such as surface roughness, surface texture, and topographical requirements. Ultraprecision machining (UPM) requirements are quite common and essential for products and components with optical finishing, including larger and highly accurate mirrors, infrared optics, laser devices, varifocal lenses, and other freeform optics that can satisfy the technical specifications of precision optical components and devices without further post-polishing. Ultraprecision machining can provide high precision, complex components and devices with a nanometric level of surface finishing. Nevertheless, the process requires an in-depth and comprehensive understanding of the machining system, such as diamond turning with various input parameters, tool features that are able to alter the machining efficiency, the machine working environment and conditions, and even workpiece and tooling materials. The non-linear and complex nature of the UPM process poses a major challenge for the prediction of surface generation and finishing. Recent advances in Industry 4.0 and machine learning are providing an effective means for the optimization of process parameters, particularly through in-process monitoring and prediction while avoiding the conventional trial-and-error approach. This paper attempts to provide a comprehensive and critical review on state-of-the-art in-surfaces monitoring and prediction in UPM processes, as well as a discussion and exploration on the future research in the field through Artificial Intelligence (AI) and digital solutions for harnessing the practical UPM issues in the process, particularly in real-time. In the paper, the implementation and application perspectives are also presented, particularly focusing on future industrial-scale applications with the aid of advanced in-process monitoring and prediction models, algorithms, and digital-enabling technologies. Full article

Purpose: To quantify the effect of levelling the corneal surface around the optical axis on the calculated values of corneal asphericity when conic and biconic models are used to fit the anterior corneal surface. Methods: This cross-sectional study starts with a mathematical simulation proving the concept of the effect that the eye’s tilt has on the corneal asphericity calculation. Spherical, conic and biconic models are considered and compared. Further, corneal asphericity is analysed in the eyes of 177 healthy participants aged 35.4 ± 15.2. The optical axis was determined using an optimization procedure via the Levenberg–Marquardt nonlinear least-squares algorithm, before fitting the corneal surface to spherical, conic and biconic models. The influence of pupil size (aperture radii of 1.5, 3.0, 4.0 and 5.0 mm) on corneal radius and asphericity was also analysed. Results: In computer simulations, eye tilt caused an increase in the apical radii of the surface with the increase of the tilt angle in both positive and negative directions and aperture radii in all models. Fitting the cornea to spherical models did not show a significant difference between the raw-measured corneal surfaces and the levelled surfaces for right and left eyes. When the conic models were fitted to the cornea, changes in the radii of the cornea among the raw-measured corneal surfaces’ data and levelled data were not significant; however, significant differences were recorded in the asphericity of the anterior surfaces at radii of aperture 1.5 mm (p < 0.01). With the biconic model, the posterior surfaces recorded significant asphericity differences at aperture radii of 1.5 mm, 3 mm, 4 mm and 5 mm (p = 0.01, p < 0.01, p < 0.01 & p < 0.01, respectively) in the nasal temporal direction of right eyes and left eyes (p < 0.01, p < 0.01, p < 0.01 & p < 0.01, respectively). In the superior–inferior direction, significant changes were only noticed at aperture radii of 1.5 mm for both right and left eyes (p = 0.05, p < 0.01). Conclusions: Estimation of human corneal asphericity from topography or tomography data using conic and biconic models of corneas are affected by eyes’ natural tilt. In contrast, the apical radii of the cornea are less affected. Using corneal asphericity in certain applications such as fitting contact lenses, corneal implant design, planning for refractive surgery and mathematical modelling when a geometrical centre of the eye is needed should be implemented with caution. Full article

We place constraints on DM sterile neutrino scalar decay production (SDP) assuming that sterile neutrinos representa fraction from the total Cold Dark Matter energy density. For the cosmological analysis we complement the CMB anisotropy measurements with CMB lensing gravitational potential measurements, that are sensitive to the DM distribution to high redshifts and with the cosmic shear data that constrain the gravitational potential at lower redshifts than CMB. We also use the most recent low-redshift BAO measurements that are insensitive to the non-linear effects, providing robust geometrical tests. We show that our datasets have enough sensitivity to constrain the sterile neutrino mass $m_{{\nu }_s}$ and the mass fraction $f_S$ inside the co-moving free-streaming horizon. We find that the best fit value $m_{{\nu }_s}=7.88\pm 0.73$ keV (68% CL) is in the parameter space of interest for DM sterile neutrino decay interpretation of the 3.5 keV X-ray line and that $f_S=0.86\pm 0.07$ (68% CL) is in agreement with the upper limit constraint on $f_S$ from the X-ray non-detection and Ly-$\alpha$ forest measurements that rejects $f_S=1$ at 3$\sigma$. However, we expect that the future BAO and weak lensing surveys, such as EUCLID, will provide much more robust constraints. Full article

The power density of femtosecond lasers and exposure time to the tissue are crucial for a successful procedure in terms of safety and precision. The reduction of the pulse duration allows reducing the quantity of the energy to be delivered to the tissue for disruption with strongly diminished mechanical and thermal collateral damage. The cutting effect of ultra-short pulses is very precise, minimally traumatic, safe, and predictable. Future developments will lead to further energy reductions to achieve optical breakdowns. However, the pulse length cannot be shortened arbitrarily because below 100 fs nonlinear effects can change the process in an unfavorable way. Compared to manual-conventional cataract surgery, femtosecond laser-assisted cataract surgery (FLACS) shows many advantages in clinical application, especially with regard to precision and tissue protection. The femtosecond laser has become particularly important and has made the overall procedure safer when we deal with complex cataract cases such as subluxated lenses. We provide an overview of the evolution of femtosecond laser technology for use in refractive and cataract surgeries. This article describes the advantages of available laser platforms with ultrashort pulses and mainly focuses on the technical and physical backgrounds of ophthalmic surgery technologies. Full article

Femtosecond (fs)-laser direct writing is a powerful technique to enable a large variety of integrated photonic functions in glass materials. One possible way to achieve functionalization is through highly localized and controlled crystallization inside the glass volume, for example by precipitating nanocrystals with second-order susceptibility (frequency converters, optical modulators), and/or with larger refractive indices with respect to their glass matrices (graded index or diffractive lenses, waveguides, gratings). In this paper, this is achieved through fs-laser-induced crystallization of LiNbO₃ nonlinear crystals inside two different glass matrices: a silicate (mol%: 33Li₂O-33Nb₂O₅-34SiO₂, labeled as LNS) and a borosilicate (mol%: 33Li₂O-33Nb₂O₅-13SiO₂-21B₂O₃, labeled as LNSB). More specifically, we investigate the effect of laser scanning speed on the crystallization kinetics, as it is a valuable parameter for glass laser processing. The impact of scanning energy and speed on the fabrication of oriented nanocrystals and nanogratings during fs-laser irradiation is studied.Fs-laser direct writing of crystallized lines in both LNS and LNSB glass is investigated using both optical and electron microscopy techniques. Among the main findings to highlight, we observed the possibility to maintain crystallization during scanning at speeds ~5 times higher in LNSB relative to LNS (up to ~600 µm/s in our experimental conditions). We found a speed regime where lines exhibited a large polarization-controlled retardance response (up to 200 nm in LNSB), which is attributed to the texturation of the crystal/glass phase separation with a low scattering level. These characteristics are regarded as assets for future elaboration methods and designs of photonic devices involving crystallization. Finally, by using temperature and irradiation time variations along the main laser parameters (pulse energy, pulse repetition rate, scanning speed), we propose an explanation on the origin of (1) crystallization limitation upon scanning speed, (2) laser track width variation with respect to scanning speed, and (3) narrowing of the nanogratings volume but not the heat-affected volume. Full article