Dominant Mechanism Research Articles

Nonlinear acoustics of an aperture under grazing flow

This work presents a mathematical model of a dynamically forced, acoustically compact aperture subject to one-sided mean grazing flow in two or three dimensions. By contrast to other simplified theoretical representations of a grazed aperture, the one proposed in this contribution considers some of the nonlinear effects a reduced order model should naturally inherit from the conservation equations governing the primary system’s dynamics. Furthermore, unlike other nonlinear developments, this one is able to reproduce the acoustic forcing amplitude dependence of the fundamental-frequency-based impedance, measured in recent experiments, without relying on empirical parameters. This nonlinear model offers further insight into the dominant physical mechanisms determining the aforementioned behaviour and allows reasonable a priori estimates of the aeroacoustic dynamics of the aperture. This could be used as a building block of more sophisticated systems or for the derivation of even simpler representations suitable for acoustic network modelling.

On the modification of tip leakage noise sources by over-tip liners

Over-Tip-Rotor (OTR) liners have been investigated over the last decades as a technology to further reduce fan broadband noise in turbofan engines. The suppression of noise with OTR liners is attributed to conventional attenuation of acoustic waves and source modification effects. This paper describes a fundamental experiment to gain a better understanding of the source modification effects and establish whether they are purely due to acoustic back-reactions or also due to hydrodynamic changes on the source. The OTR liner configuration is approximated by a static airfoil with its tip located over a flat plate containing a flush-mounted liner insert and separated from the airfoil tip by a small gap. Synchronous measurements of the far-field noise and wall pressure fluctuations on the airfoil tip have shown that the reduction of wall pressure at the airfoil tip by the liner is the dominant mechanism of noise reduction. The reduction in unsteady pressure fluctuations on the airfoil tip by the liner is mainly caused by back-reaction effects at high frequencies and hydrodynamic modifications at low- and mid-frequencies. Over-tip liners are found to alter the unsteady flow field in the gap region and weaken the flow structures responsible for the generation of tip noise. This study has shown that far-field noise predictions based on analytical models are useful to estimate the performance of over-tip liners, but a complete assessment should also include the impact of the liner on the tip-leakage flow, and, consequently, the sources of tip noise.

Hydrodynamic modelling of dynamical tide dissipation in Jupiter’s interior as revealed by Juno

Context. The Juno spacecraft has acquired exceptionally precise data on Jupiter’s gravity field, offering invaluable insights into Jupiter’s tidal response, interior structure, and dynamics, establishing crucial constraints. Aims. We aim to develop a new model for calculating Jupiter’s tidal response based on its latest interior model, while also examining the significance of different dissipation processes for the evolution of its system. We studied the dissipation of dynamical tides in Jupiter by thermal, viscous, and molecular diffusivities acting on gravito-inertial waves in stably stratified zones and inertial waves in convection ones. Methods. We solved the linearised equations for the equilibrium tide. Next, we computed the dynamical tides using linear hydrodynamical simulations based on a spectral method. The Coriolis force is fully taken into account, but the centrifugal effect is neglected. We studied the dynamical tides occurring in Jupiter using internal structure models that respect Juno’s constraints. We specifically looked at the dominant quadrupolar tidal components, and our focus is on the frequency range that corresponds to the tidal frequencies associated with Jupiter’s Galilean satellites. Results. By incorporating the different dissipation mechanisms, we calculated the total dissipation and determined the imaginary part of the tidal Love number. We find a significant frequency dependence in dissipation spectra, indicating a strong relationship between dissipation and forcing frequency. Furthermore, our analysis reveals that, in the chosen parameter regime in which kinematic viscosity and thermal and molecular diffusivities are equal, the dominant mechanism contributing to dissipation is viscosity, exceeding both thermal and chemical dissipation in magnitude. We find that the presence of stably stratified zones plays an important role in explaining the high dissipation observed in Jupiter.

Aerobic granular sludge for complex heavy metal-containing wastewater treatment: characterization, performance, and mechanisms analysis.

Complex heavy metal (HM)-containing wastewater discharges pose substantial risks to global water ecosystems and human health. Aerobic granular sludge (AGS) has attracted increased attention as an efficient and low-cost adsorbent in HM-containing wastewater treatment. Therefore, this study systematically evaluates the effect of Cu(II), Ni(II), and Cr(III) addition on the characteristics, performance and mechanism of AGS in complex HM-containing wastewater treatment process by means of fourier transform infrared spectroscopy, inductively coupled plasma spectrocopcy, confocal laser scanning microscopy, extracellular polymeric substances (EPS) fractions detection and scanning electron microscope-energy dispersive X-ray. The results showed that AGS efficiently eliminated Cu(II), Ni(II), and Cr(III) by the orchestrated mechanisms of ion exchange, three-layer EPS adsorption [soluble microbial products EPS (SMP-EPS), loosely bound EPS (LB-EPS), tightly bound EPS (TB-EPS)], and inner-sphere adsorption; notably, almost 100% of Ni(II) was removed. Three-layer EPS adsorption was the dominant mechanism through which the HM were removed, followed by ion exchange and inner-sphere adsorption. SMP-EPS and TB-EPS were identified as the key EPS fractions for adsorbing Cr(III) and Cu(II), respectively, while Ni(II) was adsorbed evenly on SMP-EPS, TB-EPS, and LB-EPS. Moreover, the rates at which the complex HM penetrated into the granule interior and their affinity for EPS followed the order Cu(II) > Ni(II) > Cr(III). Ultimately, addition of complex HM stimulated microorganisms to excrete massive phosphodiesterases (PDEs), leading to a pronounced decrease in cyclic diguanylate (c-di-GMP) levels, which subsequently suppressed EPS secretion due to the direct linkage between c-di-GMP and EPS. This study unveils the adaptability and removal mechanism of AGS in the treatment of complex HM-containing wastewater, which is expected to provide novel insights for addressing the challenges posed by intricate real wastewater scenarios.

Degradation of direct red 23 dye in a plug flow reactor with adjustable angle baffles using nano-Fe3O4: modelling and optimisation

ABSTRACT Photocatalytic degradation is a key technique in wastewater treatment, particularly for toxic dye removal, yet challenges related to poor hydrodynamics and mass transfer limitations persist. This study addresses these challenges by innovatively employing an adjustable-angle baffle in a plug flow reactor (PFR) to enhance dye removal efficiency. A lab-scale PFR with an adjustable baffle was utilised to assess the impact of various factors, including baffle angle, catalyst concentration, hydraulic retention time (HRT), pH, and initial dye concentration, on the removal of direct red 23 dye. The experimental design employed a central composite design (CCD), with subsequent data analysis using response surface methodology (RSM) and artificial neural network (ANN) models. The findings demonstrate that the adjustable baffle significantly impacts dye removal, achieving maximum efficiency at an optimal angle of 77.5 degrees. The ANN model outperformed the RSM model, with a higher determination coefficient (R 2) of 0.994 compared to 0.928. Furthermore, RSM and genetic algorithms yielded closely aligned optimal conditions, validating their accuracy. The optimised conditions achieved a dye removal efficiency of 89.47%. Significantly, the study also identified degradation as the dominant mechanism over adsorption and highlighted the impressive stability of nano-Fe3O4 during the recycling process. Mineralisation analysis revealed the presence of lightweight organic residual molecules post-treatment. These outcomes demonstrate the effectiveness of adjustable baffles in PFRs, marking a significant advancement in wastewater treatment technologies and underscoring the critical role of baffle orientation and catalyst concentration in optimising dye removal processes.

Ultrafast and Durable Sodium-Ion Storage of Pseudocapacitive VN@C Hybrid Nanorods from Metal-Organic Framework.

Vanadium nitride (VN) is a promising electrode material for sodium-ion storage due to its multivalent states and high electrical conductivity. However, its electrochemical performance has not been fully explored and the storage mechanism remains to be clarified up to date. Here, the possibility of VN/carbon hybrid nanorods synthesized from a metal-organic framework for ultrafast and durable sodium-ion storage is demonstrated. The VN/carbon electrode delivers a high specific capacity (352mA h g-1), fast-charging capability (within 47.5 s), and ultralong cycling stability (10000 cycles) for sodium-ion storage. In situ XRD characterization and density functional theory (DFT) calculations reveal that surface-redox reactions at vanadium sites are the dominant sodium-ion storage mechanism. An energy-power balanced hybrid capacitor device is verified by assembling the VN/carbon anode and active carbon cathode, and it shows a maximum energy density of 103Wh kg-1 at a power density of 113W kg-1.

Effect of raster angle on the fracture properties of additively manufactured ABS via essential work of fracture

AbstractThe increasing application of additive manufacturing (AM) technology across various sectors has sparked significant interest in characterizing 3D‐printed components. An essential aspect of achieving fracture‐resistant designs is gaining a comprehensive understanding of the fracture behavior exhibited by these components. While most studies have focused on linear‐elastic fracture mechanics (LEFM), there is a lack of comprehensive studies on the post‐yield fracture behavior (PYFM) of 3D‐printed components. As a result, this study aims to fill this gap by investigating the impact of raster angle, a critical parameter influencing fracture properties and often leading to premature failures, on the fracture properties of fused deposition modeling (FDM) 3D printed acrylonitrile butadiene styrene (ABS) using essential work of fracture (EWF). Outcomes showed that by changing lay‐ups from [90]5 to [0]5, the value of we or elastic work increased by nearly 306%. Further, the maximum and minimum values of the plastic work (βwp) were for [45/−45/45/−45/45] and [90]5 lay‐ups, in order. By changing lay‐ups from [90]5 to [45/−45/45/−45/45], the value of βwp increased by approximately 216%. In addition, the fractured surfaces of tested samples are also analyzed to provide insights into the dominant failure mechanisms for different raster angles.

BTB domain mutations perturbing KCTD15 oligomerisation cause a distinctive frontonasal dysplasia syndrome.

KCTD15 encodes an oligomeric BTB domain protein reported to inhibit neural crest formation through repression of Wnt/beta-catenin signalling, as well as transactivation by TFAP2. Heterozygous missense variants in the closely related paralogue KCTD1 cause scalp-ear-nipple syndrome. Exome sequencing was performed on a two-generation family affected by a distinctive phenotype comprising a lipomatous frontonasal malformation, anosmia, cutis aplasia of the scalp and/or sparse hair, and congenital heart disease. Identification of a de novo missense substitution within KCTD15 led to targeted sequencing of DNA from a similarly affected sporadic patient, revealing a different missense mutation. Structural and biophysical analyses were performed to assess the effects of both amino acid substitutions on the KCTD15 protein. A heterozygous c.310G>C variant encoding p.(Asp104His) within the BTB domain of KCTD15 was identified in an affected father and daughter and segregated with the phenotype. In the sporadically affected patient, a de novo heterozygous c.263G>A variant encoding p.(Gly88Asp) was present in KCTD15. Both substitutions were found to perturb the pentameric assembly of the BTB domain. A crystal structure of the BTB domain variant p.(Gly88Asp) revealed a closed hexameric assembly, whereas biophysical analyses showed that the p.(Asp104His) substitution resulted in a monomeric BTB domain likely to be partially unfolded at physiological temperatures. BTB domain substitutions in KCTD1 and KCTD15 cause clinically overlapping phenotypes involving craniofacial abnormalities and cutis aplasia. The structural analyses demonstrate that missense substitutions act through a dominant negative mechanism by disrupting the higher order structure of the KCTD15 protein complex.

Evaluation of commercial nanofiltration and reverse osmosis membrane filtration to remove per-and polyfluoroalkyl substances (PFAS): Effects of transmembrane pressures and water matrices.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are now widely found in aquatic ecosystems, including sources of drinking water and portable water, due to their increasing prevalence. Among different PFAS treatment or separation technologies, nanofiltration (NF) and reverse osmosis (RO) both yield high rejection efficiencies (>95%) of diverse PFAS in water; however, both technologies are affected by many intrinsic and extrinsic factors. This study evaluated the rejection of PFAS of different carbon chain length (e.g., PFOA and PFBA) by two commercial RO and NF membranes under different operational conditions (e.g., applied pressure and initial PFAS concentration) and feed solution matrixes, such as pH (4-10), salinity (0- to 1000-mM NaCl), and organic matters (0-10mM). We further performed principal component analysis (PCA) to demonstrate the interrelationships of molecular weight (213-499 g·mol-1 ), membrane characteristics (RO or NF), feed water matrices, and operational conditions on PFAS rejection. Our results confirmed that size exclusion is a primary mechanism of PFAS rejection by RO and NF, as well as the fact that electrostatic interactions are important when PFAS molecules have sizes less than the NF membrane pores. PRACTITIONER POINTS: Two commercial RO and NF membranes were both evaluated to remove 10 different PFAS. High transmembrane pressures facilitated permeate recovery and PFAS rejection by RO. Electrostatic repulsion and pore size exclusion are dominant rejection mechanisms for PFAS removal. pH, ionic strength, and organic matters affected PFAS rejection. Mechanisms of PFAS rejection with RO/NF membranes were explained by PCA analysis.

Sustainable large-scale Fe3O4/carbon for enhanced polystyrene nanoplastics removal through magnetic adsorption coagulation

The omnipresence of nanoplastics in natural water sources raises significant environmental and health concerns due to their challenging removal and potential to transport harmful pollutants. These particles pose threats to terrestrial and aquatic ecosystems, as well as human health, inducing inflammation and oxidative stress. In response, this study focused on an innovative Fe3O4/C nano-adsorbent, derived from discarded printer cartridge toner, for tackling the removal of polystyrene nanoplastics (PS-NPs) through magnetic adsorption coagulation (MAC) with polyaluminum chloride (PACl) as a coagulant. Extensive experimentation achieved a remarkable 99 % removal efficiency at a desirability function value of 0.868 under optimum conditions (pH = 8, adsorbent dosage 2.5 mg, contact time 2 min, PACl concentration 17.5 mg/L, PS-NPs concentration 75 mg/L) with an R2 = 0.9997, a CV% = 0.730 and an Adeq Precision = 122.837. The dominant removal mechanism involved adsorption bridging and electrostatic interaction between PS-NPs and Fe3O4/C in the presence of PACl. Findings covered adsorption kinetics, isotherms, and thermodynamics, adhering to the pseudo-second-order model (R2 = 0.996), Langmuir (R2 = 0.9912) isotherm and negative value of ΔG° (−8.899) as an endothermic adsorption process. The results demonstrated a maximum adsorption capacity of 523 mg/g, showcasing the effectiveness of the approach. Furthermore, the Fe3O4/C material exhibited robust reusability and stability, owing to its magnetite properties. The primary goal was to engineer a magnetic recoverable nano-adsorbent from discarded toner, contributing to cost reduction, streamlined coagulation processes, reduced coagulant consumption, and significantly improved micro/nanoplastics removal.

Divergence among Local Structure, Dynamics, and Nucleation Outcome in Heterogeneous Nucleation of Close-Packed Crystals.

Heterogeneous crystal nucleation is the dominant mechanism of crystallization in most systems, yet its underlying physics remains an enigma. While emergent interfacial crystalline order precedes heterogeneous nucleation, its importance in the nucleation mechanism is unclear. Here, we use path sampling simulations of two model systems to demonstrate that crystalline order in its traditional sense is not predictive of the outcome of the heterogeneous nucleation of close-packed crystals. Consequently, structure-based collective variables (CVs) that reliably describe homogeneous nucleation can be poor descriptors of heterogeneous nucleation. This divergence between structure and nucleation outcome is accompanied by an intriguing dynamical anomaly, wherein low-coordinated crystalline particles outpace their liquid-like counterparts. We use committor analysis, high-throughput screening, and machine learning to devise CV optimization strategies and present suitable structural heuristics within the metastable fluid for CV prescreening. Employing such optimized CVs is pivotal for properly characterizing the mechanism of heterogeneous nucleation in metallic and colloidal systems.

Stress relaxation cracking susceptibility evaluation in 347H stainless steel welds

AbstractStress relaxation cracking (SRC) has been reported as a dominant failure mechanism for 347H stainless steel welds at elevated service temperatures, occurring in either the heat-affected zone (HAZ) or fusion zone (FZ). In this study, SRC susceptibility of physically simulated HAZ and cross-welded E347-347H stainless steel welds was studied using a four-step accelerated SRC test with a thermomechanical physical simulator. The stress and temperature range studied represents weld-induced residual stress at 150–600 MPa and post-weld heat treatment temperatures between 800 and 1050 °C. For all temperature conditions, the cross-welded samples failed at a lower critical stress threshold than the simulated HAZ. A finite element model of a 50.8-mm-thick single-V groove weld was used to generate the residual stress maps induced by a 40-pass welding procedure, which in combination with the experimental threshold stress map predicted potential SRC failure locations. Postmortem microstructural evaluations were performed to identify contributing characteristics to SRC. It was found that HAZ samples exhibited a combination of creep void development, secondary cracks with intergranular fracture near grain boundary carbides, and eutectic phases. FZ samples showed brittle fracture with cracks propagating along straight, non-tortuous interdendritic grain boundaries.

Wear behavior of MIG manufactured 12Cr-xC (x=0.3, 0.4) hardfacings under different temperatures and loads

Metal inert gas (MIG) hardfacing technology has developed high-performance materials on carbon steel, which exhibit superior thermal wear resistance linked to Cr and C contents. In this study, the 12Cr-xC (x = 0.3, 0.4) hardfacings were manufactured by the MIG method, and the corresponding wear behavior on different loads and temperatures was characterized. The results revealed that the 12Cr-xC hardfacings exhibited good forming quality, with microstructure consist of martensite matrix, retained austenite, varying shape of the martensite-austenite continent (M/A), and a small number of carbides. The hardness reaches 483.1 and 520.3 HV0.2. The coefficient of friction (COF) of the 12Cr-xC hardfacings showed a range of 0.27-0.43 and decreased with temperature increased from 150 °C to 300 °C at 200 N. The 12Cr-xC hardfacings exhibited a good wear resistance and the wear loss rates at a low level (10-5 mm3/(N·m)). The SiC balls' worn morphology is irregular, with abrasive wear and embedded oxide debris. Adhesive wear occurs under specific conditions, with a low wear loss rate compared to hardfacings. At 150 °C, 12Cr-xC hardfacings exhibit low Whardfacing/Wball (4–11), with abrasive mechanisms. Higher loads lead to more pronounced sacrifice of SiC balls, with abrasive wear and oxides covering the worn surface at 300 °C, with tribochemical reactions being the dominant mechanism.

Effect of “M” and “B” superlattice barrier layers on dark current of long-wavelength infrared detectors

This paper studies superlattice materials with M barrier (InAs/GaSb/AlSb/GaSb superlattice) and B barrier (InAs/AlSb superlattice) structures. Firstly, it introduces the diffusion current, generation-recombination current, tunneling current and surface leakage current in devices, and analyzes the factors affecting different dark current mechanisms. Secondly, it theoretically analyzes the influence of the two barrier structures on device performance. Finally, devices were fabricated using these two structures, and the device performance was characterized. At a bias voltage of −50 mV and operating temperature of 77K. The PπMN type long-wave infrared (LWIR) detector has an RA of 91.4 Ω cm2 and a LW dark current density of 3.51 × 10−4 A cm−2. The PπBN type LWIR detector has an RA of 439 Ω cm2 and a LW dark current density of 2.81 × 10−4 A cm−2. Meanwhile, by fitting the data at different temperatures, the activation energy Ea of the PπMN type LWIR detector is 119.8 meV, with dark current mainly determined by diffusion current and generation-recombination current. The activation energy Ea of the PπBN type LWIR detector is 126.2 meV, with dark current mainly determined by diffusion current. This experimentally verifies the dominant dark current mechanisms for the two barrier structures of LWIR detectors, providing strong support for the design of superlattice detector structures.

Prediction of reverse osmosis membrane fouling in water reuse by integrated adsorption and data-driven models

In contemporary society, the reverse osmosis (RO) process is important for water treatment and reuse industry. However, membrane fouling remains a challenging issue during operation. To date, RO system operation mainly relies on the operator's knowledge, and the maintenance is carried out based on schedule or pre-defined criteria due to our limited understanding of RO fouling in real applications. To better understand the process and enable system optimization, an integrated data-driven coupled with adsorption model has been proposed in this study. The data-driven model calibrates the mechanistic model and predicts future values, while the adsorption model provides predictions on transmembrane pressure (TMP). By integrating these two models, an accurate prediction with high robustness and an insight into the detailed fouling mechanisms in real plants were achieved. In addition to the model itself, multiple regression analysis (MRA) had also been applied to identify the dominant fouling mechanisms. This analysis confirms that it is highly possible that membrane fouling is developed from an intermediate pore blockage to cake filtration.

Effect of strain rate on compressive behavior and deformation mechanism of CoCrNi medium entropy alloy fabricated via cold spray additive manufacturing

The equiatomic CoCrNi medium entropy alloy (MEA) has shown better mechanical properties than many MEAs and high entropy alloys (HEAs) at room temperatures. However, the mechanical behaviors and deformation mechanisms of CoCrNi MEAs have yet to be studied, especially at different strain rates. In this study, cold spray additive manufacturing (CSAM) was applied to fabricate freestanding CoCrNi deposits. The investigation of compressive behaviors and deformation mechanisms were studied at a low-strain rate of 0.001 s−1 and at a high strain rate ranging from 2300 s−1to 4200 s−1. The as-fabricated sample exhibited refined grains, unfused powders, and large porosity, resulting in limited metallurgical bonding within the bulk CoCrNi deposit and deformed particle interface. Therefore, post-heat treatment at 1350 °C was applied to improve the interparticle bonding and strengthen the as-fabricated CoCrNi deposits. As expected, the annealed deposit significantly improved the ultimate compressive strength (UCS) and strain elongation of the as-fabricated deposits from ∼90 MPa and ∼5% to ∼1400 MPa, and ∼70% at a strain rate of 0.001 s−1. Besides, the annealed samples showed improvement twofold in UCS and ductility of the as-fabricated deposits from ∼67 MPa and ∼8.6% to ∼1266 MPa and ∼34% at a strain rate of 4200 s−1 and 3800 s−1 respectively. The TEM image of the annealed CoCrNi sample showed deformation twining, nano twins, planar slips, and microbands, which are the dominant deformation mechanisms that help to promote the plasticity and the work hardening behavior of this alloy. This work validates the compressive behavior and deformation mechanism of cold-sprayed CoCrNi MEA associated with post-heat treatment at different strain rates.

Ultrasound assisted removal of methylene blue using functionalized mesoporous biochar composites

Global wastewater pollution issues demands developing innovative and cost-efficient techniques for wastewater treatment. The current study reports application of different metal oxide (iron, copper, zinc) doped carbon-based materials such as activated carbon (AC), groundnut shell (GS), cotton stalk (CS) and biochar (BC) for the removal of methylene blue (MB). Iron oxide-doped AC exhibited significantly higher adsorption capacity (∼32 mg/g) with all the other metal oxide-doped AC having the adsorption capacity below ∼10 mg/g. Adsorption of MB on FeCS followed the Freundlich isotherm, suggesting multilayer adsorption on the heterogeneous active sites. Kinetic models indicated dominant chemisorption mechanisms, aligning well with the pseudo-second-order model. Higher adsorption capacity under alkaline pH conditions is attributed to the prevalence of negative charges on the surface. The presence of ultrasound further intensified the adsorption behavior resulting in a maximum removal efficiency of ∼90 % within 10 min. An optimum adsorbent loading of 0.5 g/L was determined for effective removal of MB. FeCS adsorbent displayed stable performance over multiple cycles, affirming its reliability for reuse. These results shed light on the practical application of biochars derived from large scale pyrolysis process for the wastewater remediation.

P-Incorporation Induced Enhancement of Lattice Oxygen Participation in Double Perovskite Oxides to Boost Water Oxidation.

Activating the lattice oxygen in the catalysts to participate in the oxygen evolution reaction (OER), which can break the scaling relation-induced overpotential limitation (> 0.37V) of the adsorbate evolution mechanism, has emerged as a new and highly effective guide to accelerate the OER. However, how to increase the lattice oxygen participation of catalysts during OER remains a major challenge. Herein, P-incorporation induced enhancement of lattice oxygen participation in double perovskite LaNi0.58Fe0.38P0.07O3-σ (PLNFO) is studied. P-incorporation is found to be crucial for enhancing the OER activity. The current density reaches 1.35mA cmECSA -2 at 1.63V (vs RHE), achieving a sixfold increase in intrinsic activity. Experimental evidences confirm the dominant lattice oxygen participation mechanism (LOM) for OER pathway on PLNFO. Further electronic structures reveal that P-incorporation shifts the O p-band center by 0.7eV toward the Fermi level, making the states near the Fermi level more O p character, thus facilitating LOM and fast OER kinetics. This work offers a possible method to develop high-performance double perovskite OER catalysts for electrochemical water splitting.

Unraveling the mystery of antibiotic resistance genes in green and red Antarctic snow

Antarctic snow is a thriving habitat for a diverse array of complex microorganisms, and can present in different colors due to algae blooms. However, the potential role of Antarctic snow as reservoirs for antibiotic resistance genes (ARGs) has not been studied. Using metagenomic sequencing, we studied ARGs in green-snow and red-snow on the Fildes Peninsula, Antarctica. Alpha and beta diversities of ARGs, as well as co-occurrence between ARGs and bacteria were assessed. The results showed that a total of 525 ARGs conferring resistance to 30 antibiotic classes were detected across the samples, with half of the ARGs presented in all samples. Green-snow exhibited a higher number of ARGs compared to red-snow. The most abundant ARGs conferring resistance to commonly used antibiotics, including disinfecting agents and antiseptics, peptide, isoniazid, MLS, fluoroquinolone, aminocoumarin, etc. Multidrug resistance genes stood out as the most diverse and abundant, with antibiotic efflux emerging as the dominant resistance mechanism. Interestingly, the composition of ARGs in green-snow markedly differed from that in red-snow, highlighting distinct ARG profiles. Beta-diversity partitioning showed a higher contribution of nestedness for ARG's variation in green-snow, while higher contribution of turnover in red-snow. Furthermore, the co-occurrence analysis between ARGs and bacteria unveiled intricate relationships, indicating that certain ARGs may have multiple potential hosts. The observed differences in co-occurrence networks between green-snow and red-snow suggested distinct host relationships between ARGs and bacteria in these colored snows. Given the increasing appearance of the colored snow around the world due to the climate change, the results shed light on the mystery and potential implication of ARGs in green and red Antarctic snow.

Ultrafast photocarrier dynamics in InAs/GaAs self-assembled quantum dots investigated via optical pump-terahertz probe spectroscopy

Optical pump-terahertz probe (OPTP) spectroscopy was performed to measure the lifetime of photogenerated carriers in the barrier and the wetting layer (WL) regions of an indium arsenide on gallium arsenide (InAs/GaAs) single-layer self-assembled quantum dot (QD) sample. A modified rate equation model of carrier dynamics was proposed where possible state-filling in both QD and WL is considered. Drude model fitting was also performed to extract the time-dependent plasma frequency and phenomenological scattering time from the terahertz transmission spectra. The results of the OPTP experiment show two prominent recombination processes that occur at different timescales after photoexcitation. These two processes were attributed to carrier recombination in the GaAs barrier and the quantum well-like states of the WL based on the fitted lifetimes. Calculations using the coupled differential rate equations were also able to replicate the experimental trend at low fluence. The lack of agreement between experimental data and numerical calculations at high optical fluence was mainly attributed to the possible saturation of the GaAs density of states. Lastly, the results of the parameter fitting for the plasma frequency and scattering time indicate a transition from the barrier to the WL recombination as the dominant carrier recombination mechanism within the time scale of the OPTP scan. This further lends credence to the proposed model for carrier dynamics in SAQD systems under state-filling conditions.