Uniform Distribution Research Articles

Hygroscopic Mg–Al LDHs composite microspheres for highly efficient hyperspectral camouflage in the VIS and NIR wavebands

In order to enhance the hyperspectral camouflage efficacy of stealth coatings against a natural vegetative backdrop, LiCl, known for its significant hygroscopic properties, was incorporated into green Mg–Al layered double hydroxide (Mg–Al LDHs) material. Micron-sized composite microspheres were subsequently synthesized via the spray-drying granulation technique. The structure, morphology, and chemical composition of these microspheres were thoroughly characterized by X-ray diffraction, scanning electron microscopy, laser particle size analysis, nitrogen adsorption–desorption isotherms, and Fourier-transform infrared spectroscopy. The effect of LiCl content on the moisture absorption capacity and near-infrared reflectance spectra of the microspheres was systematically evaluated. We found that incorporating an optimal amount of LiCl into the internal pores of the Mg–Al LDHs microspheres did not compromise their smooth surface morphology and uniform particulate distribution. Notably, when the LiCl content was 10%, the maximum saturation moisture uptake ratio of the coating increased to 0.75 g/g. This hygroscopicity significantly enhanced the absorption and scattering of near-infrared radiation by the coating while concurrently improving its ability to modulate the shape and reflectance of both the visible and near-infrared spectral curves. Spectral congruence between the synthetic coating and natural green foliage was quantified at 97.41%. Moreover, this performance was maintained over 10 cycles of programmed drying and re-humidification, and the coating consistently demonstrated stable hygroscopic properties and sustained over 95% spectral congruence. These optimized artificial coatings were found to effectively confuse hyperspectral classification algorithms, thus blending seamlessly into a natural foliage backdrop. This study provides a new method for regulating VIS and NIR spectral (visible–near infrared spectrum) features, which will be critical for applications in advanced hyperspectral camouflage materials.

The effect of CoPt3 sublayer on the formation of fct-L10 FePt nanoparticles in direct synthesis method

The smaller the size of magnetic nanoparticles is, the less their coercivity will be. The magnetic coercivity of FePt nanoparticles, in the compound ordered phase, known as fct-L10 FePt, is up to the order of tesla; however, the temperature of 600 °C, required for the formation of this phase, increases the size of FePt nanoparticles. In this research, fct-L10 FePt nanoparticles were fabricated using the direct synthesis method by Co-sputtering system. The presence of a CoPt3 sublayer resulted in the formation of a fct-L10 phase of FePt nanoparticles at 400 °C with a uniform surface distribution and mean size and standard deviation of 11 nm and 1.5 nm, respectively. The same as the other results of FePt/CoPt3, magnetic coercivity of fct-L10 FePt nanoparticles, with the mentioned size, reached to 3.0 kOe at room temperature, because of the presence of the CoPt3 sublayer.

Evolution of Long-Term Load Reduction Using Borrowed Soil

AbstractThe effectiveness of load-reduction techniques often diminishes due to creep behavior observed in geomaterials, as loess backfill is used, the load reduction rate of high-filled cut-and-cover tunnels (HFCCTs) after creep will decrease by 10.83%, posing a threat to the long-term stability of deeply buried structures such as HFCCTs. Therefore, a geotechnical solution is crucial to ensuring sustained effectiveness in load-reduction strategies over time. This study utilizes a finite-difference method to examine three promising measures for mitigating creep effects. Our analysis focuses on the time-dependent changes in earth pressure atop the cut-and-cover tunnel (CCT) and the internal distribution of cross-sectional forces, including bending moment, shear force, axial force, and displacement. Results indicate that the creep behavior of load-reduction materials significantly influences the internal force distribution. Furthermore, sustained load reduction is achieved when utilizing low-creep materials like dry sandy gravel as backfill soil, which needs to be borrowed from other sites. Additionally, integrating concrete wedges with load-reduction techniques facilitates a more uniform stress distribution atop CCTs.

Achieving Homogeneous Microstructure and Superior Properties in High-N Austenitic Stainless Steel via a Novel Atmosphere-Switching Method

Powder metallurgy is widely used to fabricate high-nitrogen, nickel-free austenitic stainless steel. However, after sintering and nitriding, additional solution treatment is typically required to achieve uniform nitrogen distribution and a homogeneous austenite phase. This work proposes a novel method to eliminate the need for lengthy and high-temperature solution treatment by switching the nitrogen atmosphere to argon during the cooling process. The effects of different N2-Ar atmosphere-switching temperatures (750–1320 °C) on the phase composition, element distribution, microstructure, mechanical properties, and corrosion resistance of the studied steels were systematically investigated. Results show that cooling in the N2 atmosphere initially transforms the matrix to a fully austenitic structure enriched with nitrogen. Excessive nitrogen infiltration leads to Cr2N precipitation, inducing partial austenite decomposition and forming a multiphase structure comprising austenite, α-Fe, and Cr2N. Strategic switching from N2 to Ar reverses this reaction, yielding a high-nitrogen, chemically uniform austenitic structure. Specifically, switching at 1150 °C, the steel exhibits excellent mechanical properties and corrosion resistance, with a yield strength of 749 MPa, an ultimate tensile strength of 1030 MPa, an elongation of 38.7%, and a corrosion current of 0.06 mA/cm2, outperforming the steels cooled solely in N2 and subsequently solution-treated. This novel method offers advantages in cost reduction, energy saving, and operational effectiveness, highlighting its potential for broad industrial application.

Achieving Homogeneous Microstructure and Superior Properties in High-N Austenitic Stainless Steel via a Novel Atmosphere-Switching Method

Powder metallurgy is widely used to fabricate high-nitrogen, nickel-free austenitic stainless steel. However, after sintering and nitriding, additional solution treatment is typically required to achieve uniform nitrogen distribution and a homogeneous austenite phase. This work proposes a novel method to eliminate the need for lengthy and high-temperature solution treatment by switching the nitrogen atmosphere to argon during the cooling process. The effects of different N2-Ar atmosphere-switching temperatures (750–1320 °C) on the phase composition, element distribution, microstructure, mechanical properties, and corrosion resistance of the studied steels were systematically investigated. Results show that cooling in the N2 atmosphere initially transforms the matrix to a fully austenitic structure enriched with nitrogen. Excessive nitrogen infiltration leads to Cr2N precipitation, inducing partial austenite decomposition and forming a multiphase structure comprising austenite, α-Fe, and Cr2N. Strategic switching from N2 to Ar reverses this reaction, yielding a high-nitrogen, chemically uniform austenitic structure. Specifically, switching at 1150 °C, the steel exhibits excellent mechanical properties and corrosion resistance, with a yield strength of 749 MPa, an ultimate tensile strength of 1030 MPa, an elongation of 38.7%, and a corrosion current of 0.06 mA/cm2, outperforming the steels cooled solely in N2 and subsequently solution-treated. This novel method offers advantages in cost reduction, energy saving, and operational effectiveness, highlighting its potential for broad industrial application.

Effect of laser-assisted irradiation on plasma electrolytic oxidation of titanium alloys: Arc spot evolution characteristics and photoelectric synergistic mechanisms

Laser irradiation can be employed as an auxiliary energy field to optimize functional plasma electrolytic oxidation (PEO) coatings. Herein, the mechanism of the effect of laser-assisted irradiation on the morphology and composition of ceramic coatings prepared by PEO of titanium alloys in electrolytes with sodium tetraborate-based is discussed from the perspective of plasma arc spot evolution and photoelectric synergistic effect. X-ray diffraction (XRD), transmission electron microscopy (TEM), Mott-Schottky (M-S), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to analyze the coating characteristics. The results showed that laser-assisted irradiation promoted the oxidation of the coatings, accelerated the conversion of the anatase phase to the rutile phase, reduced the oxygen vacancy defects and formed the "ant nest" porous microstructure. Monitoring of the voltage, electric field, and plasma discharge arc spot indicated that laser-assisted irradiation restricted the electric field diffusion on the anode surface, reduced the termination voltage, and significantly increased the intensity (maximum discharge percentage increased from 14.238 % to 20.358 %) and uniformity of distribution of the plasma discharge. Instantaneous photoresponse curves and electrochemical impedance spectroscopy confirmed that the PEO coatings exhibited fast and sustained photoelectric response under simultaneous laser irradiation, progressively enhanced with increasing laser irradiation energy. The photogenerated electrons excited by the semiconductor TiO2 coating under the simultaneous irradiation of laser can be used as the initial carriers of the electron avalanche, which induces the generation of a plasma on the surface of the anode and thus enhances the plasma discharge behavior, which is the fundamental reason for the optimization of the coating characteristics.

Enhanced activity of electrodeposited WO3 thin films as bi-functional electrocatalysts for water splitting

The ultimate goal of the hydrogen economy is to develop an efficient and cost-effective electrocatalyst that can accelerate hydrogen synthesis from water without or with little additional energy. This study describes a unique surface modified electrodeposited nano-sized tungsten oxide (WO3) as an intriguing bi-functional electrocatalyst for OER in alkaline and HER in acidic conditions. The nano-WO3 was synthesized hydrothermally and electrodeposited on a fluorinated tin oxide (FTO) electrode. The highly uniform distribution of the WO3@FTO catalyst results in negligible charge transfer resistance, a large electroactive surface area, and increased water-splitting potential. During oxygen evolution reaction (OER), electrodeposited WO3@FTO initiates water splitting at an overpotential (η) of just 240 mV and represents a turnover frequency (TOF) of 0.59 sec−1. These results are comparable to previously reported electrocatalysts. Under an alkaline electrolyte, a current density of 15 mA/cm2 remained constant for several hours, indicating the high stability and durability of the electrodeposited WO3@FTO electrode. The electrode also performed well in hydrogen evolution reactions (HER). A Tafel slope of 46 mV/dec and −28 mV/dec was found for OER and HER, respectively, indicating an enhanced kinetics rate of reaction taking place at the electrode surface. Furthermore, in acidic conditions, the electrode represents a lower HER overpotential of 104 mV. The work provides a significant understanding of electrodeposited WO3@FTO electrodes and their role in electrochemical water splitting.

Application of CFD Simulation to the Design of an Innovative Drying Chamber

Drying and sanitising equipment has been very common in industrial plants since the pandemic. These are devices that consume significant amounts of energy. The best solution is to use a drying chamber equipped with a heat pump, which allows partial recovery of the energy. In the design of the drying chamber, the drying time is important, which depends both on the parameters of the heat pump itself, and the geometry and airflow of the drying chamber. The geometry and airflow supply should be arranged to ensure a uniform distribution of velocity throughout the drying area. For this purpose, the use of CFD simulations has been proposed. A model was developed in ANSYS/FLUENT where all model parameters, including the optimal mesh density, turbulence models, etc., were determined. The model was verified on the experimental results of the basic design of the chamber. Then an innovative design was proposed that was modelled and optimised in terms of the distribution of the inlet’s perforation. The final design was made, and, at the same time, the simulation’s results were verified by measuring the velocity of airflow in the new design. Together with the optimisation of the heat pump, this made it possible to reduce the drying time by 50%, with a simultaneous reduction in the energy consumed.

Efficient hydrodeoxygenation of lignin-derived phenolic compounds over bifunctional catalyst comprising H4PMo11VO40 coupled with Ni/C.

In the catalytic transformation of bio-oil into liquid fuels having alkanes via hydrodeoxygenation (HDO), the acid and metal sites in the catalyst are pivotal for promoting the HDO of lignin-derived phenolic compounds. This study introduces a novel bifunctional catalyst comprising phosphomolybdenum-vanadium heteropolyacids (H4PMo11VO40) coupled with Ni/C. The HDO reaction of the model compound guaiacol was carried out under reaction conditions of 230 °C, revealing the superior performance of H4PMo11VO40 with Ni/C catalysts compared to the conventional acids, even at low dosage. The Keggin structure of H4PMo11VO40 provided a solid catalyst with strong acidic and redox properties, alongside advantages such as ease of synthesis, cost-effectiveness, and tunable acid and redox properties at the molecular level. Characterization of Ni/C and the prepared acid demonstrated favorable pore structure with a mesopore volume of 0.281 cm3/g and an average pore size of 3.404 nm, facilitating uniform distribution and catalytic activity of Ni-metal. Incorporating acid enhances the acidic sites, fostering synergistic interactions between metal and acidic sites within the catalyst, thereby significantly enhancing HDO performance. Guaiacol conversion at 230 °C reached 100%, with a cyclohexane selectivity of 89.3%.This study presents a promising pathway for convertinglignin-derived phenolic compounds.

Anomalous Conductive Properties of Polymer Composites with Carbon Nanotubes: Why Power Laws Are Not Universal

The conductive properties of CNT/polymer composites have been extensively studied. However, the impact of CNT distribution in the matrix on the composite polarization remains underexplored and poorly understood. Since it is difficult to achieve a uniform distribution of CNTs in polymers, most researchers have focused only on indiscriminately aggregated states. In this article, a new blending method was suggested to prepare a series of epoxy resin-based composite samples with varying levels of CNT uniformity/aggregation and the same filling fractions. Notably, the permittivity values turned out to be inversely related to the composite uniformity: the lowest permittivity values were obtained in the most uniform formulation, and vice versa. With 0.1% CNT, the real part values of the most uniform and aggregated samples were 6.6 and 16.2 at 107 Hz and 11.6 and 370.5 at 101 Hz, respectively. For the filler content of 0.1–0.5%, the conductive properties were largely determined by the distribution of CNTs and not their content. Within the entire frequency range, the uniform sample with 0.2% CNT exhibited significantly lower permittivity than the aggregated sample with 0.1% CNT. These findings emphasize the importance of the aggregation factor and underscore the non-universality and limitations of the percolation theory and power laws. The observed phenomenon is best explained by the micro-capacitor model, or the Maxwell–Wagner polarization, and suggests that a significant portion of the literature in the field needs to be reconsidered.

Experimental investigation of porous gyroid structure: Effect of cell size and porosity on performance

This paper presents an experimental investigation of three triply periodic minimal surface based gyroid sheet samples with varying cell size and porosity. The thermal and hydraulic performances of the samples were analyzed and compared under different design parameters (cell size and porosity). The experimental results revealed that the gyroid structures achieved uniform temperature distribution, allowing for the disruption of the thermal boundary layer and enhancing heat transfer. The gyroid structure characterised by small cell size and low porosity (Gyroid-A: 15 mm/0.75) dissipates more heat from its surface compared to the structure with large cell size and high porosity (Gyroid-C: 32 mm/0.9). Gyroid-A also exhibits higher Nusselt number and convection heat transfer coefficient with 51.5 % increase as compared to Gyroid-C. In addition, Gyroid-A has the lowest thermal resistance (with maximum of 45.4 % reduction) and the highest specific pressure drop as compared to the other gyroid structures. Moreover, Gyroid-A exhibits lower total entropy generation (75.9 % reduction) and higher overall performance evaluation criteria, PEC (more efficient heat transfer in relation to flow resistance) as compared to Gyroid-C. The experimental results of this work is important for the design and optimization of heat transfer applications utilizing gyroid sheet structures for effective heat dissipation.

Acoustics-driven multifunctional microreactor bioinspired by Phylum Porifera for bidirectional pumping and mixing production of silica nanofluids

The Phylum Porifera is one of the most primitive multicellular animals without a mouth, digestive cavity, or central nervous system. Its pores are strewn with flagella inside. Phylum Porifera wiggles its flagella to inhale the seawater, which brings in oxygen, bacteria, microscopic algae, and other organic debris to feed on. Inspired by this natural system, a microreactor based on sharp-edge has been developed and applied in microfluidics to achieve bidirectional pumping and mixing. Here we demonstrate a multifunctional microreactor for bidirectional pumping and mixing that mimics the internal flagella of the Phylum Porifera. The microreactor is designed based on microscale nonlinear acoustics to achieve functionalities via the acoustic streaming generated by the vibration of sharp-edge under the acoustic field. Numerical simulation is conducted to investigate the effect of sharp-edge numbers, dip angles, spreading angles, spacing of sharp-edges, and channel width on the pumping performance. And the bidirectional pumping is verified by experiments. Similarly, numerical simulation and experimental validation are conducted to investigate the effect of flow rate, amplitude, and sharp-edge density on mixing performance. Finally, to verify the application potential and good mixing performance of the developed microreactor, silica nanofluids were synthesized with excellent stability and uniform particle size distribution. These results not only provide important guidelines for the rational design of functional nanomaterials, but also shed new light on the development of efficient microreactors.

A semi-cellular Z-type Gate SOI-LDMOS with Improved Gate Control Capability

A Semi-cellular Z-type Gate SOI-LDMOS (ZG LDMOS) with Improved Gate Control Capability is proposed, and its physical mechanism is studied by SENTAURUS. It is a semi-cellular structure similar to "Z" consisting of a Trench Gate (TG) and a Planar Gate (PG). At the on-state, the inversion layer of the conductive channel is not only formed at the top of the P-well region, but also formed along the side wall of the Z Gate, expanding the width of the channel, improving the electron injection ability and reducing the specific on-resistance (Ron,sp). In addition, the Z Gate can also form a uniform current distribution from the drift region to the bottom, which is helpful to reduce the Ron,sp, improve the transconductance and enhance the current control ability. The 3D simulation results show that BV, Ron,sp are 187.3 V and 4.45 mΩ cm2, respectively. The FOM reached 7.91 MW/cm2. Compared with the conventional LDMOS, the FOM value of ZG LDMOS increased by 58.8 %, which breaks through the silicon limit of RESURF.

Constructing high-performance micro fuel electrodes for reversible proton ceramic electrochemical cells

Reversible proton ceramic electrochemical cells (R-PCECs) are of great interest as efficient energy conversion device. Optimization of structural design can enhance the mechanical properties and gas transport of the cells, resulting in improved electrochemical performance. In this study, we developed a 7-channel micro-monolithic R-PCEC for the first time, with uniform channel distribution and smaller gas diffusion pathway length using phase inversion/extrusion technique. The assembled cell with Ni-BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (Ni-BZCYYb, fuel electrode support) | BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb, electrolyte) | PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF, air electrode) structure showed a peak power density of 0.94 W cm−2 at 700 °C in fuel cell mode and electrolysis current density of 2.17 A cm−2 at 700 °C with an operating voltage of 1.3 V. Additionally, electrochemical impedance spectroscopy (EIS) further indicated that the diffusive polarization of the structured cell was effectively reduced compared to single-channel counterpart.

Characterizing of PVA/CMC/MWCNTs nanocomposite films doped Zn0.9Ni0.1S nanoparticles for comprehensive γ-ray radiation shielding performance

Nanocomposite films were prepared from Carboxymethylcellulose (CMC), Polyvinyl alcohol (PVA) polymers and multi-walled carbon nanotubes (MWCNTs) using the casting technique. The resulting PVA/CMC/MWCNTs nanocomposite films have been incorporated with various concentrations of the Zn0.9Ni0.1S nanoparticles. The γ-ray radiation shielding capabilities of the films were discussed in details for various gamma sources using the Phy-X/PSD software in the energy range (0.015–15 MeV). The linear (LAC) and mass (MAC) attenuation parameters, the half-value layer (HVL), the tenth value layer (TVL), the effective atomic number (Zeff) were determined. The γ-ray buildup factors, were also determined for different penetration depths in the range (0.5–40 MFP). Results showed that, the shielding parameters are greatly affected by the density of the samples and the PVA/CMC/MWCNTs samples have the highest shielding ability in the energy region ranges (0.015–0.2 MeV) and (5–15 Mev). The structural and chemical characteristics of the films and the nanoparticles were examined using X-ray diffraction technique. The films elemental composition and morphology were discussed using energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscope (SEM) techniques, respectively. The linear and nonlinear optical properties, including the extinction coefficient (K), the energy gap (Eg), the refractive index (n), the dielectric parameters, nonlinear susceptibilities(χ(1), χ(3)) and nonlinear refractive index (n2), were discussed by UV–Vis spectroscopy's absorbance and transmittance spectra. A reduction in Eg values from 4.55 eV to 4.5 eV and 4.41 eV for films doped with 1 wt% and 3 wt% of Zn0.9Ni0.1S. The uniform distribution of the added nanoparticles at 5 wt% has been confirmed. The energy dispersion parameters confirmed a higher probability of electronic transitions at low energy due to the intermolecular modifications.

Gas-Solid flow and mass transfer characteristics in activated carbon adsorption equipment: The impact of structural outline

The efficacy of adsorption of volatile organic compounds (VOCs) in industrial emissions by activated carbon (AC) is influenced by adsorption kinetics and hydrodynamics. To simulate the performance of continuous flow AC adsorption process, a computational fluid dynamics (CFD) model that includes both multiphase flow and adsorption kinetics was developed. Because of its well-understood adsorption mechanism, N-butane was chosen as the target contaminant in this investigation. Simulation results revealed that velocity distribution uniformity is deeply affected by structural outline. According to simulations of the heat and mass transfer process, the adsorption reaction stoichiometric constraints between n-butane and AC were achieved; however, full utilization of AC was difficult to reach because of the hindered heat accumulation and mass transfer diffusion. Different structural outline leads to a 2.15 % improvement of adsorption efficiency due to an enhancement in the velocity distribution uniformity. The CFD model adequately describes the breakage curve occurring in the gas-solid multiphase flow system and confirms that heat and mass transfer is the rate limiting step in contaminant adsorption. This article investigates the effects of velocity distribution, heat and mass transfer on adsorption efficiency in equipment with different structural outline, and provide valuable insights into the design and application of equipment for eliminating VOCs.

A comparative study of different algorithms and scalarization techniques for constructing the Pareto front of multiobjective optimization problems

This paper presents an analysis and comparison of various algorithms applied to different scalarization methods for multiobjective optimization problems (MOPs). At first, some theoretical results are provided on the relation between (weakly) efficient solutions of an MOP and optimal solutions of the related numerical method. Moreover, we consider some deficiencies in different scalarization approaches given in the literature and try to fill some gaps in these works. Hence, by considering appropriate limitations, we provide sufficient conditions for (ε-)properly efficient and (ε-)efficient solutions of an MOP via scalarization techniques. Then, an algorithm for approximating the Pareto front of MOPs is presented. The main purpose of this algorithm is to generate efficient points on the Pareto front with a uniform distribution. One advantage of this algorithm, compared to some other algorithms, is that in each iteration of the algorithm, more than one efficient point located on the Pareto border can be generated. The new algorithm is implemented by applying the modified Pascoletti–Serafini, the unified direction, and the modified normal boundary intersection scalarization techniques, and then the procedures are considered on different test problems including (non-)convex and discrete Pareto fronts. The capability of the numerical method is shown by comparing the results with the algorithms in the literature. To compare the algorithms, measures of coverage and spacing metric indicators are used.

Experimental study of parchment coffee drying using the combined fluidization and microwave process: Analysis of drying curves and thermal imaging

In this study, several experimental drying conditions for parchment coffee were investigated using microwave-assisted fluidization. The experiments were carried out in a prototype equipment consisting of a multimode microwave equipment (700 W and 2.45 GHz frequency) with a drying chamber inside of the cavity. Fluidization was provided by a centrifugal blower (1500 rpm nominal) operating at different controlled speeds. The experimental design corresponded to three microwave power levels (0, 210 and 350 W) and different air speeds (0, 1.7 and 3.4 m/s) at 25 and 40 °C. The experimental moisture evolution and temperature distribution showed that fluidization homogenizes the temperature profiles. Thermographic images further indicated that intermediate microwave power levels (210 W) achieved high uniformity in surface temperature distribution. The combination of fluidization and microwaves facilitated a significant acceleration of the drying rate without exceeding temperature limits, thus preventing any adverse effects on the final product's quality.

Polycyclic aromatic hydrocarbon emission in galaxies as seen with JWST

ABSTRACT We present a systematic study of mid-infrared spectra of galaxies including star-forming galaxies and active galactic nuclei observed with JWST MIRI-MRS and NIRSpec-IFU. We focus on the relative variations of the 3.3, 6.2, 7.7, 11.3, 12.7, and 17 $\mu$m polycyclic aromatic hydrocarbon (PAH) features within spatially resolved regions of galaxies including NGC 3256, NGC 7469, VV 114, II Zw96, and NGC 5728. Using theoretical PAH models and extending our earlier work, we introduce a new PAH diagnostic involving the 17 $\mu$m PAH feature. To determine the drivers of PAH band variations in galaxies, we compare observed PAH spectral bands to predictions from theoretical PAH models. We consider extinction, dehydrogenation, and PAH size and charge as possible drivers of PAH band variations. We find a surprising uniformity in PAH size distribution among the spatially resolved regions of the galaxies studied here, with no evidence for preferential destruction of the smallest grains, contrary to earlier findings. Neither extinction nor dehydrogenation play a crucial role in setting the observed PAH bands. Instead, we find that PAH charge plays a significant role in PAH inter-band variations. We find a tight relation between PAH charge and the intensity of the radiation field as traced by the [Ne iii]$/$[Ne ii] maps. In agreement with recent JWST results, we find a predominance of neutral PAH molecules in the nuclei of active galaxies and their outflows. Ionized PAHs are the dominant population in star-forming galaxies. We discuss the implications of our findings for the use of PAHs as ISM tracers in high redshift galaxies.

Polycyclic aromatic hydrocarbon emission in galaxies as seen with JWST

ABSTRACT We present a systematic study of mid-infrared spectra of galaxies including star-forming galaxies and active galactic nuclei observed with JWST MIRI-MRS and NIRSpec-IFU. We focus on the relative variations of the 3.3, 6.2, 7.7, 11.3, 12.7, and 17 $\mu$m polycyclic aromatic hydrocarbon (PAH) features within spatially resolved regions of galaxies including NGC 3256, NGC 7469, VV 114, II Zw96, and NGC 5728. Using theoretical PAH models and extending our earlier work, we introduce a new PAH diagnostic involving the 17 $\mu$m PAH feature. To determine the drivers of PAH band variations in galaxies, we compare observed PAH spectral bands to predictions from theoretical PAH models. We consider extinction, dehydrogenation, and PAH size and charge as possible drivers of PAH band variations. We find a surprising uniformity in PAH size distribution among the spatially resolved regions of the galaxies studied here, with no evidence for preferential destruction of the smallest grains, contrary to earlier findings. Neither extinction nor dehydrogenation play a crucial role in setting the observed PAH bands. Instead, we find that PAH charge plays a significant role in PAH inter-band variations. We find a tight relation between PAH charge and the intensity of the radiation field as traced by the [Ne iii]$/$[Ne ii] maps. In agreement with recent JWST results, we find a predominance of neutral PAH molecules in the nuclei of active galaxies and their outflows. Ionized PAHs are the dominant population in star-forming galaxies. We discuss the implications of our findings for the use of PAHs as ISM tracers in high redshift galaxies.