Search Results (251)

We present a theoretical study focused on the photoelectron spectrum of near-infrared (NIR) laser-driven ionization of hydrogen atoms by attosecond pulse trains composed of several HHs of the former. We analyze the effects of increasing the intensity of the NIR probe laser to account for the interference of multiple quantum pathways arising from mainbands formed in ionization by the attosecond pulse train within the strong-field approximation (SFA) beyond the commonly used first-order perturbative (in the NIR laser intensity) reconstruction of attosecond beating by interference of two-photon transitions (RABBIT). The structure of the energy bands formed in the photoelectron spectrum is governed by quantum interferences of the photoelectron wave packet released within one optical cycle of the NIR probe laser field—intracycle interference—and by the number of active high harmonic components, leading to higher-order Fourier contributions as a function of the NIR–XUV relative phase delay. We show that Fourier terms can be interpreted in terms of well-defined semiclassical trajectories. Our results demonstrate a significant departure from the standard two-path quantum-interference RABBIT picture, showing that both the phase-dependent oscillations of mainbands and sidebands and the extracted phase delays depend strongly on the probing laser intensity. The predictions of the SFA reveal that the above-threshold ionization bands exhibit systematic splitting and oscillation patterns as a function of the NIR intensity. SFA predictions are compared with results obtained within ab initio solutions of the time-dependent Schrödinger equation (TDSE), showing an excellent agreement, which evidences the minor effect of the Coulomb potential of the remaining ion on the escaping photoelectron for high energy above-threshold ionization. The precise study of the SFA reference phases is essential for the determination of the effect of the Coulomb potential on the escaping photoelectron for what these findings provide new insights into attosecond chronoscopy in the strong-field regime. Full article

Concerns about human exposure to micro- and nanoplastics (MNPLs), particularly nanoplastics (NPLs), have intensified in recent years. Consequently, there is a growing need for validated quantitative analytical methods capable of assessing NPLs in complex human biological matrices. Current approaches for NPL analysis are still limited by the absence of standardised protocols, difficulties in avoiding background contamination, and challenges associated with the selective identification and quantification of polymer-specific nanoparticles. Moreover, most common approaches for quantification by particle counting cannot be applied for NPLs < 500 nm. In this study, we developed and validated an analytical method for the detection and quantification of NPLs in human faeces. As an initial step, polyethylene (PE) and polypropylene (PP) nanoparticles (NPs) were synthesised using bottom-up methods and characterised by dynamic light scattering (DLS) and electron microscopy (SEM and TEM). To optimise and assess the extraction, synthetic faeces were prepared and used in spiking experiments to avoid background contamination from plastics. Two digestion strategies were evaluated: (i) Fenton’s reagent followed by strong acid digestion, and (ii) alkaline digestion. Quantitative determination of polymer-specific NPLs was performed by size-exclusion liquid chromatography coupled with high-resolution mass spectrometry and atmospheric-pressure photoionization (SEC-APPI-HRMS). Polymer identification was based on characteristic monomer-loss patterns and Kendrick Mass Defect analysis. Fenton-based digestion showed superior performance, yielding recoveries about 55–66% for PE and 59–61% for PP. The validated method achieved limits of detection and quantification of 0.015 and 0.058 μg/kg for PE, and 0.025 and 0.083 μg/kg for PP, respectively. Precision, expressed as %RSD, was 10.1% for PE and 20.1% for PP. These results demonstrate that SEC-APPI-HRMS combined with Fenton-based digestion provides a sensitive and reliable approach for the quantification of polymer-specific NPLs in human faeces. The method represents an important advance for human biomonitoring studies and supports future research aimed at assessing human exposure and the potential health risks associated with nanoplastics. Full article

Laser-induced breakdown in water-rich biological media results from the interplay between primary photoionization processes and avalanche amplification of free electrons. Understanding this competition is essential for predicting ablation thresholds under ultrashort-pulse irradiation. In this work, we develop an analytical rate-equation model for the buildup of electron density in water-like biological tissues. It combines photoionization and chromophore ionization into a single seed-generation term, while avalanche ionization is described through a cascade gain factor. This formulation provides a framework for describing cascade electron-impact ionization processes in liquid-like media under strong-field excitation. Our approach gives an analytical expression for the temporal evolution of electron density driven by a Gaussian laser pulse and makes it possible to separate the contributions of direct ionization of water and ionization of chromophore centers. The analytical results are compared with numerical simulations that include carrier diffusion, bimolecular recombination and trapping. The comparison clarifies the roles of seed formation and cascade amplification in the growth of the electron population. The predicted dependence of threshold fluence on pulse duration agrees well with experimental data reported for water-like tissues such as the corneal tissues at a wavelength of 800 nm. The model provides a simple analytical picture of ultrafast plasma formation and electron-driven energy deposition in water-like biological media. Full article

It is well known that gas sensor responses are affected by the presence of humidity in the analyzed gas. This is particularly true when dealing with biological fluid samples, whose high moisture content interferes with the adsorption of the trace volatile organic compounds (VOCs) on the sensors’ active layer. To address this challenge, this study focuses on designing and testing a novel sampling system for the dehumidification of biological fluid headspace to be characterized by an electronic nose (e-Nose). Such a system, based on the use of disposable polymeric sampling bags purged with dry air, exploits the polymers’ permeability to water vapor to reduce sample humidity. Tested materials included Nalophan^TM (20 μm), high-density polyethylene (HDPE, 8, 9, 10 and 11 μm), low-density polyethylene (LDPE, 12 and 50 μm), and biodegradable polyester (Bio-PS, 15 μm). First, dehumidification performance was characterized as a function of dry air flow rate and film type. A purge of 1 L/min accelerated the sample humidity removal compared to passive storage of bags from >2 h to <1 h (from 80% to 20% RH). Second, a mass-balance model was applied to dedicated experiments to decouple water losses due to diffusion and adsorption, showing that diffusion through the polymer wall dominates, while adsorption occurs in the early stages of conditioning. Third, because these materials are not selectively permeable to water, potential loss of water-soluble VOCs during dehumidification was investigated. Pooled urine headspace samples—both raw and spiked with a metabolite mix of VOCs—were dried using each material and analyzed using a photo-ionization detector (PID) and an e-Nose. Results were compared against a Nafion^TM dryer. Comparison was based on the e-Nose’s ability to discriminate between pooled vs. spiked samples and reveal real-life metabolomic changes. Nalophan^TM bags and Nafion^TM dryer provided the highest VOC fingerprint to support discrimination by the e-Nose, while Bio-PS provided the fastest sample dehumidification. The proposed bag-based system offers a cost-effective, disposable, and contamination-free solution to humidity interference in e-Noses. Full article

Aging underground pipeline infrastructure across the United States, including systems used for potable water supply, wastewater collection, and stormwater conveyance, has exceeded its intended service life, emphasizing the need for replacement or rehabilitation to maintain reliable service to communities. Among available trenchless technologies, cured-in-place pipe (CIPP) is widely applied because it minimizes surface disruption and is well-suited for use in densely populated areas. Despite these advantages, environmental concerns remain regarding the release of total volatile organic compounds (VOCs) during CIPP installation and curing. This study evaluates total VOC emissions from CIPP liners under field conditions. Air samples were collected at six installation sites across the United States before, during, and after installation and curing to quantify key VOC species. Multiple sampling methods were employed, including photoionization detectors (PIDs), Summa canisters, and personal worker sampling. The measured compounds included styrene, cumene, acetophenone, hexane, toluene, and ethanol. Measured concentrations were compared with occupational exposure limits established by the U.S. Environmental Protection Agency (USEPA), the National Institute for Occupational Safety and Health (NIOSH), and the Occupational Safety and Health Administration (OSHA). The results indicate that styrene was the dominant compound within active CIPP work zones, with peak concentrations reaching 25.5 ppm during curing. In contrast, VOC concentrations decreased substantially within five feet downwind of the work zone. Overall, the findings suggest that potential public exposure risks are limited, while workers directly involved in CIPP operations may experience elevated short-term exposures during installation and curing activities. Full article

Photoionization detector (PID) sensors are widely used for ambient Volatile organic compound (VOC) monitoring because they are inexpensive, flexible, and fast. However, PID outputs are strongly influenced by environmental conditions (especially temperature and relative humidity) and exhibit substantial inter-sensor variability, limiting their quantitative reliability. Here we present a rapid machine-learning calibration workflow that maps PID signals and meteorological covariates to a photochemically relevant reference metric, PTR-derived VOC OH reactivity (R_OH,PTR, s⁻¹), calculated from online PTR-ToF-MS VOC measurements weighted by OH reaction rate constants. Four MiniPID sensors were co-located with a PTR-ToF-MS and a thermohygrometer, and data were harmonized to 10-s resolution. Multiple regression models were evaluated, with ensemble methods (RF and XGBoost) providing the best overall performance. To ensure realistic generalization under temporal autocorrelation, validation used a time-aware split: models were trained on a contiguous 24-h co-location period and evaluated on subsequent days (out-of-time). In this out-of-time evaluation, XGBoost achieved strong agreement with R_OH,PTR across sensors (Pearson’s r = 0.85, R² = 0.64, RMSE = 1.74 s⁻¹), while substantially improving inter-sensor consistency. This short-duration calibration approach supports practical co-location-based harmonization of PID networks for high-temporal-resolution VOC reactivity monitoring in urban and industrial environments. Full article

Thermal oxidation of edible oils during high-temperature cooking produces complex fumes containing harmful volatile compounds. However, the role of water, a common co-reactant in practical cooking, remains insufficiently understood. In this study, oleic acid was used as a model compound to investigate thermal oxidation. Online monitoring using synchrotron radiation photoionization mass spectrometry (SR-PIMS) revealed that water significantly increased the emission of volatile acetaldehyde and acrolein, with maximum increases of 164% and 123% at 10% water addition. Complementary offline GC-MS analysis showed enhanced formation of (E)-2-decenal, (E,E)-2,4-decadienal, and (E)-2-undecenal, suggesting these unsaturated aldehydes may be key intermediates. Mechanistically, oleic acid underwent free radical-mediated peroxidation to form (E)-2-decenal, (E)-2-undecenal, and (E,E)-2,4-decadienal. These intermediates subsequently decomposed into acetaldehyde and acrolein via hydration, retro-aldol condensation, and hydroperoxide scission, with water accelerating both processes. Overall, these findings highlight water’s critical role in promoting the generation of harmful volatile aldehydes in oil fumes. Full article

We report experimental measurements of the absolute photoionization cross sections for chlorine ions in different stages of ionization, over photon energy ranges corresponding to the L-shell (2s and 2p subshells) excitations. Single, double and triple photoionization channels were investigated for the ions Cl⁺, Cl²⁺, Cl³⁺ and Cl⁴⁺. The measurements were performed on the PLéIADES beamline at the SOLEIL radiation storage ring facility, using the Multi-Analysis Ion Apparatus (MAIA). Resonance energies and line strengths are provided for the isonuclear sequence and the evolution of the inner shell photoionization behaviour is demonstrated for the chlorine ions as the degree of ionization is increased. While dominated by photoionization from the corresponding ground state ions, the photoion yields may also contain contributions from low-lying metastable states. The results provide useful data on these ions for plasma modelling and can serve as benchmarking experimental data for future atomic theoretical calculations. Full article

Recent advances in non-local thermodynamic equilibrium (non-LTE) plasma simulations, for example in modeling kilonova ejecta, have emphasized the need for consistent and reliable atomic data. Unlike LTE modeling, non-LTE calculations must include a consistent treatment of various photon-induced and collisional processes in order to describe realistic electron and photon distributions in the plasma. However, the available atomic data are often incomplete, inconsistently formatted, or even fail to indicate the main dependencies on the level structure and plasma parameters, thus limiting their practical use. To address these issues, we have extended Jac, the Jena Atomic Calculator (version v0.3.0), to provide direct access to relevant cross sections, plasma rates, and rate coefficients. Emphasis is placed on photoexcitation and ionization processes as well as their time-reversed counterparts—photo-de-excitation and photorecombination. Whereas most of these data are still based on empirical expressions, their dependence on the ionic level structure and plasma temperature is made explicit here. Moreover, the electron and photon distributions can be readily controlled and adjusted by the user. This transparent representation of atomic data for photon-mediated processes, together with a straightforward use, facilitates their integration into existing plasma codes and improves the interpretation of high-energy astrophysical phenomena. It may support also more accurate and flexible non-LTE plasma simulations. Full article

We present a time-dependent nonperturbative theory of the reconstruction of attosecond beating by interference of multiphoton transitions (RABBIT) for photoelectron emission from hydrogen atoms in the transverse direction relative to the laser polarization axis. Extending our recent semiclassical strong-field approximation (SFA) model developed for parallel emission, we deduce analytical expressions for the transition amplitudes and demonstrate that the photoelectron probability distribution can be factorized into interhalf- and intrahalfcycle interference contributions, the latter modulating the intercycle pattern responsible for sideband formation. We identify the intrahalfcycle interference arising from trajectories released within the same half cycle as the mechanism governing attosecond phase delays in the perpendicular geometry. Our results reveal the suppression of even-order sidebands due to destructive interhalfcycle interference, leading to a characteristic spacing between adjacent peaks that doubles the standard spacing observed along the polarization axis. Comparisons with numerical calculations of the SFA and the ab initio solution of the time-dependent Schrödinger equation confirm the accuracy of the semiclassical description. This work provides a unified framework for understanding quantum interferences in attosecond chronoscopy, bridging the cases of parallel and perpendicular electron emission in RABBIT-like protocols. Full article

To overcome the limitations of lengthy laboratory testing cycles and insufficient on-site responsiveness, this study developed an online rapid monitoring device for volatile organic compounds (VOCs) in soil–water–air systems based on photoionization detection (PID) technology. The device integrates modular sensor units, incorporates an electromagnetic valve-controlled multi-medium adaptive switching system, and employs an internal heating module to enhance the volatilization efficiency of VOCs in water and soil samples. An integrated system was developed featuring “front-end intelligent data acquisition–network collaborative transmission–cloud-based warning and analysis”. The effects of different temperatures on the monitoring performance were investigated to verify the reliability of the designed system. A polynomial fitting model between concentration and voltage was established, showing a strong correlation (R² > 0.97), demonstrating its applicability for VOC detection in environmental samples. Field application results indicate that the equipment has operated stably for nearly three years in a mining area of Shandong Province and an industrial park in Anhui Province, accumulating over 600,000 valid data points. These results demonstrate excellent measurement consistency, long-term operational stability, and reliable data acquisition under complex outdoor conditions. The research provides a distributed, low-power, real-time monitoring solution for VOC pollution control in mining and industrial environments. It also offers significant demonstration value for standardizing on-site emergency monitoring technologies in multi-media environments and promoting the development of green mining practices. Full article

We present a time-dependent framework that combines a hybrid basis, consisting of Gaussian-type orbitals (GTOs) and finite-element discrete-variable representation (FEDVR) functions, with a multicenter grid to simulate strong-field and attosecond dynamics in atoms and molecules. The method incorporates the construction of the orthonormal hybrid basis, the evaluation of electronic integrals, a unitary time-propagation scheme, and the extraction of optical and photoelectron observables. Its accuracy and robustness are benchmarked on one-electron systems such as atomic hydrogen and the dihydrogen cation (${\mathrm{H}}_2^{+}$) through comparisons with essentially-exact reference results for bound-state energies, high-harmonic generation spectra, photoionization cross sections, and photoelectron momentum distributions. This work establishes the groundwork for its integration with quantum-chemistry methods, which is already operational but will be detailed in future work, thereby enabling ab initio simulations of correlated polyatomic systems in intense ultrafast laser fields. Full article

The control of mechanical effects, such as shock waves, induced by ultrashort laser pulses in water is crucial for applications in biomedicine and material processing. However, optimizing these effects requires a detailed understanding of how laser parameters, particularly pulse duration, influence the underlying energy deposition mechanisms. This study systematically investigates the dependence of shock wave amplitude on fluence (up to 10 J/cm²) and pulse duration (200 fs to 10 ps) of near-infrared laser pulses under tight focusing conditions (Numerical aperture NA = 0.42), using a combined experimental and numerical approach based on the dynamical rate equation model. Our key finding is that the shock wave amplitude is governed by the total kinetic energy of the electrons in the laser-induced plasma, leading to a distinct maximum at approximately 5 ps (confidence interval: 4.5–5.5 ps) and saturation at fluences ~7 J/cm². This optimum arises from a balance between the increasing effectiveness of avalanche ionization for longer pulses and the competing effects of electron recombination and reduced photoionization efficiency. Consequently, these results identify a practical parameter window—pulse durations of 4–6 ps at moderate fluences—for optimizing laser-induced mechanical effects in applications such as laser surgery in aqueous media. Full article

Accurate determination of opacity is critical for understanding radiation transport in both astrophysical and laboratory plasmas. We employ atomic data from R-Matrix calculations to investigate radiative properties in high-energy-density (HED) plasma sources, focusing on opacity variations under extreme plasma conditions. Specifically, we analyze environments such as the base of the convective zone (BCZ) of the Sun ($2\times {10}^6$ K, $N_e={10}^{23}$/cc), and radiative opacity data collected using the inertial confinement fusion (ICF) devices at the Sandia Z facility ($2.11\times {10}^6$ K, $N_e=3.16\times {10}^{22}$/cc) and the Lawrence Livermore National Laboratory National Ignition Facility. We calculate Rosseland Mean Opacities (RMO) within a range of temperatures and densities and analyze how they vary under different plasma conditions. A significant factor influencing opacity in these environments is line and resonance broadening due to plasma effects. Both radiative and collisional broadening modify line shapes, impacting the absorption and emission profiles that determine the RMO. In this study, we specifically focus on electron collisional and Stark ion microfield broadening effects, which play a dominant role in HED plasmas. We assume a Lorentzian profile factor to model combined broadening and investigate its impact on spectral line shapes, resonance behavior, and overall opacity values. Our results are relevant to astrophysical models, particularly in the context of the solar opacity problem, and provide insights into discrepancies between theoretical calculations and experimental measurements. In addition, we investigate the equation-of-state (EOS) and its impact on opacities. In particular, we examine the “chemical picture” Mihalas–Hummer–Däppen EOS with respect to level populations of excited levels included in the extensive R-matrix calculations. This study should contribute to improving opacity models of HED sources such as stellar interiors and laboratory plasma experiments. Full article

Enhancing indoor environmental quality while reducing building energy consumption represents a critical challenge for sustainable building design, particularly in hot arid climates where cooling loads dominate energy use. Despite extensive research on green wall systems (GWSs), robust quantitative data on their combined impact on air quality and thermal performance in real-world office environments remains limited. This research quantified the synergistic effects of an active indoor green wall system on key indoor air quality indicators and cooling energy consumption in a contemporary office environment. A comparative field study was conducted over 12 months in two identical office rooms in Dhahran, Saudi Arabia, with one room serving as a control while the other was retrofitted with a modular hydroponic green wall system. High-resolution sensors continuously monitored indoor CO₂, volatile organic compounds via photoionization detection (VOC_PID; isobutylene-equivalent), and PM2.5 concentrations, alongside dedicated sub-metering of cooling energy consumption. The green wall system achieved statistically significant improvements across all parameters: 14.1% reduction in CO₂ concentrations during occupied hours, 28.1% reduction in volatile organic compounds, 20.9% reduction in PM2.5, and 13.5% reduction in cooling energy consumption (574.5 kWh annually). Economic analysis indicated financial viability (2.0-year payback; benefit–cost ratio 3.0; 15-year net present value SAR 31,865). Productivity-related benefits were valued from published relationships rather than measured in this study; base-case viability remained strictly positive in energy-only and conservative sensitivity scenarios. Strong correlations were established between evapotranspiration rates and cooling benefits (r = 0.734), with peak performance during summer months reaching 17.1% energy savings. Active indoor GWSs effectively function as multifunctional strategies, delivering simultaneous air quality improvements and measurable cooling energy reductions through evapotranspiration-mediated mechanisms, supporting their integration into sustainable building design practices. Full article