Air Molecules Research Articles

Dimensional accuracy of acrylonitrile butadiene styrene and polylactic acid samples printed in vacuum-assisted material extrusion system

This paper discusses the impact of integrating a vacuum system into a material extrusion 3D printing process for acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) materials. The study aimed to investigate the effect of a vacuum system on the dimensional accuracy of the printed samples. Upon completion of the printing process, the samples’ dimensions were carefully assessed using a Coordinate Measuring Machine (CMM). The geometrical dimensions measured are the diameter, corner radius, fillet, thickness, width, length and angle. Based on the result obtained, the material has yet to reach 100% of the desired geometry, which was identified due to the shrinkage of the material after the printing process. The results show that the vacuum system improved material flow and reduced dimensional deviations by reducing air molecules and minimizing convection. The results indicated a significant enhancement in dimensional accuracy for both ABS and PLA samples when using the vacuum system. ABS samples showed a 4% increase in accuracy, while PLA samples exhibited a 2% improvement compared to samples printed without vacuum assistance. These improvements were achieved by optimizing process parameters such as layer height (0.15 mm), infill percentage (10%), printing speed (45 mm s−1), and bed temperature (60 °C). These parameters were selected to ensure finer details, improved precision, structural support, stability, better adhesion, and reduced warping.

Self Consistent Modeling of Relativistic Runaway Electron Beams Giving Rise to Terrestrial Gamma‐Rays Flashes

AbstractTerrestrial Gamma Ray Flashes (TGFs) are short bursts of gamma rays occurring during thunderstorms. They are believed to be produced by Relativistic Runaway Electron Avalanches (RREAs). In this paper, we present a new numerical model based on the Particle‐In‐Cell (PIC) method to simulate the interactions between the electromagnetic fields and the electron avalanche self‐consistently. The code uses a cylindrical Yee lattice to numerically solve the electromagnetic fields, a Monte Carlo approach to simulate collisions with air molecules, and a plasma fluid model to calculate the effects of low‐energy electrons and ions. The model is first tested through the reproduction of dispersion relations in a hot plasma. RREAs propagating under a homogeneous background electric field are then simulated. Owing to the self‐consistent nature of this description, we report here new physical properties such as saturation processes in the electron density and in the number of high‐energy electrons, detailed dynamical screening of the electric field in the ion trail of the avalanche, and the associated electric currents. We find that the saturation of RREAs is obtained when the numbers of high‐energy electrons and photons is consistent with those believed to be representative of TGF sources.

Finite Element Mode-ling of Damping of a Squeeze Gas Film in High-Frequency Microelectromechanical Switches with Capacitive Contact

The damping effects of a squeeze gas film are one of the main components of damping and naturally arise in the designs of dynamic micromechanical devices, in particular, in high-frequency micromechanical switches with an electrostatic activation mechanism, in which the electrostatic drive consists of a fixed electrode in the form of a plate and a movable electrode in the form of a movable plate suspended on elastic suspensions for the case of capacitive contact. In the static mode of the device, a thin film of gas consisting of air molecules or other inert gas surrounding the device is located and held between the electrodes of the electrostatic drive. This article presents a mathematical model based on the obtained linear inhomogeneous Reynolds differential equation and performs finite element modeling of the pressure distribution in the plate of a suspended movable electrode during compression of a gas film during electrostatic activation of micromechanical switches with a capacitive contact and parallel arrangement of the electrodes of an electrostatic drive depending on the magnitude of the coefficient of this component of damping in a three-dimensional coordinate system, the dependences between the damping force and the elastic force of the compressible gas film on the value of the damping coefficient are also presented. The presented results are applicable to assess the effect of isothermal damping of a squeeze gas film on the dynamics of micromechanical devices, in particular, on the dynamic characteristics of high-frequency micromechanical switches with an electrostatic activation mechanism and a capacitive contact.

A Numerical Simulation of PFPE Lubricant Kinetics in HAMR Air Bearing

This report investigates the kinetics of lubricant molecules in the HAMR air bearing to understand the initiation and growth of PFPE contamination on the head surface. The collisions with the air bearing induce three forces—drag, thermophoresis, and lift. Of these, we find that lift forces are negligible. Then, a sensitivity analysis of the remaining two forces reveals the conditions where they dominate. Further, a hybrid simulation strategy is utilized to track their movements. The results show that the contaminations (smear) highly depend on the interplay between the thermophoresis and drag forces. We then explain the mechanism of the formation of the various observed patterns. Finally, we offer some recommendations to exploit the air bearing to contain smear on the head.

Adsorption and gas sensitive behavior of Co2+ doped TiO2(101) crystal planes

Density functional theory (DFT) and Electrochemical Impedance Spectroscopy (EIS) were used to study the molecular adsorption behavior of the Co2+ doped TiO2(101) crystal plane, and the ethanol molecular gas sensitivity test was performed. Theoretical models indicate that doping leads to oxygen defects on the crystal plane and further chemisorption of two oxygen molecules, resulting in reduced electrical conductivity and improved oxygen storage capacity on the crystal plane. Ethanol molecules do not compete with N2, O2, and H2O molecules on doped crystal planes because of their different adsorption active sites, which means that the response time of gas-sensitive detection of ethanol molecules is short and is not interfered with the air molecules in the test environment. These results were confirmed by EIS and gas sensitivity experiments. The change of electrical conductivity after the adsorption of molecules on the crystal plane was confirmed by EIS. The enhanced oxygen storage capacity of the doped crystal plane was confirmed by the expansion of the linear response range of gas-sensitive detection from 20-100 ppm before doping to 20–1200 ppm. This provides a scientific basis for effectively shortening the gas-sensitive response time, increasing the concentration range, improving the oxygen-carrying capacity, and enhancing the catalytic and gas-sensitive properties of the material.

Efficient detection of lung cancer biomarkers using functionalized transition metal dichalcogenides (MoS2) Monolayers: DFT study

Selective sensing properties of transition metal dichalcogenides (MoX2, X = S, Se) towards specific volatile organic compounds (VOCs) associated with lung-cancer are investigated using state-of-the-art density-functional theory (DFT) methods. In the present investigation, a combination of DFT and the non-equilibrium Green’s functions (NEGF) formalism are employed to probe the sensing of four VOCs; namely: (i) Isoprene “C5H8”, (ii) Toluene “C7H8”, (iii) Cyclopropanone “C3H4O”, and (iv) Isopropanol “C3H8O”; and four interfering air molecules CO2, H2O, N2 and O2. We find that the doping of single atom of selected transition metals (TMs = Mn, Fe, Ni, Cu) can enhance both the sensitivity and the selectivity of MoX2. Our results show that the selectivity is rather distinct towards the detection of VOCs when TMs doping is targeting the chalcogenide site. Adsorption energies, charge transfers, electronic properties through density of states and band structures, and the sensor responses are obtained in all the cases, particularly for C5H8 and C3H8O, which show superior selectivities. Enhanced selectivity is attributed to the enhancement in the polarity of the substrate after the TMs doping targeting the chalcogenide sites. Our work demonstrates the potential of MoX2 based single atom catalysts as efficient biosensor towards the specific VOCs for the early diagnosis of lung cancer.PACS Numbers: 31.15.E-, 68.43.-h, 68.43.Fg, 82.33.Pt, 87.15.Aa, 87.15.Kg, 87.19.Xx, 87.19.xj.

Potential high-performance H[formula omitted] gas sensors based on monolayer 2D metal oxide [formula omitted]-MoO[formula omitted] doped with Pt/Rh[formula omitted]predicted by DFT calculations

High-performance H2 gas sensors based on monolayer 2D metal oxide α-MoO3 doped with Pt/Rh has been predicted. With a binding energy of −5.262 eV/−5.877 eV, the substitutional doping of Pt/Rh for Mo is a stable doping. After adsorbing O2 in air, the band gap of Pt/Rh-α-MoO3 decreases by 0.62 eV/0.51 eV due to the appearance of the impurity levels and the band narrowing effect. Due to such large decrease, electrons in the valence band can be excited more easily into the conduction band to produce more O2(ads)−, which would oxidize more H2 to generate H2O or hydroxyl along with releasing more electrons to the sensor and increasing the sensor’s sensitivity. First losing electrons through adsorbing O2 molecules in air and then obtaining electrons through adsorbing H2 molecules in H2, the charge variation of the sensor based on monolayer Pt/Rh-α-MoO3 is 1.487 e/0.394 e for per O2/H2, which suggests that the sensor may have higher sensitivity and lower detection limit. The larger charge variation is also confirmed by the shift of the Fermi level towards the higher energy direction after adsorbing H2.

First-principles study on the stability and degradation of the lead-free double perovskite materials Cs2B'BiCl6 (B' = Li, Na, K) under natural environment

The stability of perovskite solar cell materials in the natural environment is crucial to their commercial application. Understanding the detailed interaction mechanism between the air or water molecules (H2O) and the perovskite materials is a key way to explore their stabilities. In this study, we evaluate the geometric stabilities and thermodynamic stabilities of the lead-free Cs2B'BiCl6 (B' = Li, Na, K) double perovskite materials, and further explore the effect of air and H2O molecules on the stability and degradation of the Cs2B'BiCl6 double perovskite materials. The calculated results indicate that the pristine Cs2B'BiCl6 materials possess good geometric stabilities and thermodynamic stabilities. Under natural environment, the N2, O2, and CO2 gas molecules hardly penetrate into Cs2LiBiCl6 and Cs2NaBiCl6 because of positive absorption energies, while N2 and O2 can easily penetrate into Cs2KBiCl6 due to negative absorption energies. In contrast, the H2O molecules can easily penetrate into all Cs2B'BiCl6 double perovskite materials with negative absorption energies. Furthermore, the penetration of H2O molecules causes structural deformations of the double perovskites and the resultant rotation or rupture of some octahedra. Further simulations of H2O molecules adsorption on the surface of the double perovskites reveal that the adsorption energies of H2O molecules at all adsorption sites are negative, indicating that the Cs2B'BiCl6 double perovskite materials are prone to absorb H2O molecules in a humid environment. Therefore, the H2O molecules are the main factor affecting the stability and degradation of all Cs2B'BiCl6 double perovskite materials. Additionally, Cs2KBiCl6 shows much worse stability, which is responsible for the scarcely experimental reports on its synthesis and characterization.

Advancements in nanotechnology for acoustic management in pickleball

This research investigates the use of advanced nano-fiber technology for sound and noise management in pickleball courts. The technology, known for its flexibility and adaptability, addresses the unique acoustic challenges of pickleball, a sport with a distinctive noise profile characterized by impulsive and unpredictable sounds. These nano-fibers are particularly effective in absorbing mid to high-frequency noises (800–5000 Hz) common in pickleball. Incorporating these nano-fibers into acoustic foams and textiles significantly enhances sound absorption, allowing for thinner materials while doubling performance compared to conventional materials. These fibers, about 1/500th the diameter of human hair, have a high surface area to volume ratio, aiding in sound scattering and increased friction with air molecules. This structure enables the efficient transformation of sound energy into heat, which is then effectively dissipated. Aligned with the Acoustical Society of America's standards, this abstract emphasizes a scientific breakthrough in sports acoustics, contributing to the reduction in urban noise pollution. The study underscores the impact of cutting-edge material technology in improving environmental acoustics and community well-being.

Vantage Points: Essays, Critical Perspectives, Field Notes

Museum artifacts can be imagined as “vibrant matter” (Bennett 2010).1 Indeed, it could be argued that one function of museums and exhibitions may well be to create circumstances that let us experience material objects as inspiring, vital, and “vibrant”—a term that incidentally links all matter to those vibrations of air molecules that we call “sound.” But what is it that makes objects vibrant?

Numerical Analysis of Narrow-gap Underfill Flow in the Flip-chip Process Using the Lattice Boltzmann Method

Flip-chip packaging is a first-level interconnect technology, and to predict its melt front of capillary driven underfill analytical models have been made. Using the Analytical models, prediction of the melt front can be efficiently done, however it is difficult to reflect the flow resistance resulting from complex solder bump arrangement. Therefore, 3D numerical analysis is required. In this study, Lattice Boltzmann method (LBM) is used for observing the micro void generation that occurs in a underfill process with a height of several tens of microns. LBM statistically expresses the motion of the molecule, to solve the mass transfer of the microscale. In particular, LBM has strengths in multiphase flow analysis of several microscales that cannot be solved by continuum assumption. In this paper, underfill process of several tens of micro scales, which was not covered in previous 3D numerical analysis studies, was simulated using LBM. The improvement of the new LBM model, which more accurately simulates the resistance due to pressure by considering collisions between air and molten mold molecules, is introduced. With the hydraulic diameter greatly reduced due to the narrow gap, it is observed how the solder bump pitch affects the micro void generation. And it is observed whether the air ventilation could change significantly according to the ambient pressure.

Linear enhancement of mechanical compliance by zeolite filling in a compact loudspeaker

A zeolite filling in the rear cavity of a compact loudspeaker enhances the sound pressure amplitude of the loudspeaker system with a frequency range up to ∼500 Hz, but its intrinsic mechanisms remain elusive. We theoretically consider the gas adsorption–desorption behavior on zeolite that can be dynamically perturbed by sound pressure from the diaphragm of the loudspeaker. By merging equivalent circuit theory with gas thermodynamic theory, a linear relationship between mechanical compliance and zeolite volume in the rear cavity is quantitatively modeled. Confirmed by electroacoustic impedance experiments, the linear relationship with a slope of 1.92 mF cm−3 reveals the intrinsic ability of porous material to enhance mechanical compliance by adsorption of gas onto the zeolite in the rear cavity. This study correlates the kinetic behavior of air molecules on zeolite and acoustic behavior; it offers a novel insight to improve the performance of a compact loudspeaker by simple filling with porous material and introduces a comprehensive method for evaluating gas adsorption–desorption dynamics in porous media.

Direct Assembly of Aerogel Micro‐Nanofiber/MXene Sponges with Dual‐Network Structures for All‐Day Personal Heating

AbstractMaintaining human body temperature under low temperature is crucial to human well‐being, thereby urgently requiring for high‐performance warmth retention materials. However, designing such materials with both mechanical robustness and warming up the human body under complex and changing outdoor environments remains challenging. Here, a dual‐network structured aerogel micro‐nanofiber/MXene sponge is directly synthesized by the synchronous occurrence of electrospinning and electrospraying. Tailoring phase inversion of the solution jet creates micro‐nanofibers with highly porous aerogel structures, which exhibit nanoscale aperture (30–60 nm) and high single fiber surface aera (56.5 m2 g−1). Under strong hydrogen bonding interaction, the dual‐network structures are constructed by chemical entanglement between aerogel micro‐nanofibers and self‐assembled MXene networks, achieving robust stretchable and compressible property. The nanopores of the single fiber cause the Knudsen effect to suppress the slippage of air molecules, thereby enhancing the unique capacity to block heat energy. Further integrating passive radiative heating and active heating performance of MXene networks, the as‐designed sponge offers an all‐day personal heating system to rise human skin temperature over 3.5 °C. This work may provide new candidates for the applications within aerospace, energy, transportation, and building.

Light stabilizer-modified hydrocharging melt-blown nonwovens with superior charge stability for air filtration

Particulate matter poses substantial risks to human health, air visibility, climate, and ecological equilibrium. Electret materials are instrumental in air purification and personal protection, as they significantly enhance filtration efficiency without increasing pressure drop. Despite these advantages, developing electret filters with both high filtration efficiency and stable performance under thermal conditions and prolonged storage has proven challenging. In this study, we introduce a novel electret melt-blown filter fabricated through hydrocharging technology supplemented with the light stabilizer UV3346. The interaction of water and air molecules with melt-blown fibers generated abundant positive and negative charges, thereby amplifying the electrostatic attraction effect. Concurrently, UV3346 mitigated the formation of reactive free radicals and minimized charge exchanges, thus enhancing charge storage stability. Owing to the incorporation of UV3346, the UV3346/PP-0.8 melt-blown nonwovens, having a basis weight of 22 g/m2, demonstrated a filtration efficiency of 99.55 %, a low pressure drop of 59.45 Pa, and marginal decrease in filtration efficiency after heat treatment at 130 °C. Notably, the filtration efficiency experienced only a 0.30 % reduction after a two-year storage period, markedly outperforming commercial alternatives. This study is expected to inform future work on high-performance air filtration materials suitable for both air purification and personal protection equipment.

Ab initio investigation of functionalization of titanium carbide Ti3C2 MXenes to tune the selective detection of lung cancer biomarkers

Selected volatile organic compounds (VOCs), such as benzene (C6H6), cyclohexane (C6H12), isoprene (C5H8), cyclopropanone (C3H4O), propanol (C3H8O), and butyraldehyde butanal (C4H8O), in exhaled human breath can act as indicators or biomarkers of lung cancer diseases. Detection of such VOCs with low density would pave the way for an early diagnosis of the disease and thus early treatment and cure. In the present investigation, the density-functional theory (DFT) is applied to study the detection of the mentioned VOCs on Ti3C2TX MXenes, saturated with the functional groups Tx = O, F, S, and OH. For selectivity, comparative sensing of other interfering air molecules from exhaled breath, such as O2, N2, CO2, and H2O is further undertaken. Three functionalization (Tx = O, F, and S) are found promising for the selective detection of the studied VOCs, in particular Ti3C2O2 MXenes has shown distinct sensor response toward the C5H8, C6H6, C6H12, and C3H4O. The relatively strong physisorption (Eads≅-0.45to-0.65eV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${E}_{ads}\\cong -0.45 to-0.65 {\ ext{eV}}$$\\end{document}), triggered between VOC and MXene due to an enhancement of van der Waals interaction, is found responsible to affect the near Fermi level states, which in turn controls the conductivity and consequently the sensor response. Meanwhile, such intermediate-strength interactions remain moderate to yield small desorption recovery time (of order τ≅μs-ms)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au \\cong \\mu {\ ext{s}}-{\ ext{ms}})$$\\end{document} using visible light at room temperature. Thus, Ti3C2O2 MXenes are found promising candidate material for reusable biosensor for the early diagnosis of lung cancer diseases through the VOC detection in exhaled breath.

Spatiotemporal Control of Polymorphic Phase Transition of Glycine Crystals by Three-Dimensional Femtosecond Laser Ablation Processing.

Spatiotemporal control of the polymorphic phase transition of glycine crystals was demonstrated by three-dimensional (3D) processing with a focused femtosecond laser pulse as an external stimulus. We found that the transition from a metastable form (β-form) to more stable ones (α- or γ-form) could be triggered from the irradiated area of not only the surface but also inside of glycine crystals. This 3D processing with a focused femtosecond laser pulse enabled us to precisely monitor the transition dynamics from a targeted position to the entire part of crystals. The systematic study with the space-selective phase transition method revealed that the phase transition inside of glycine crystals was significantly slower (e.g., ∼50 times) than that at the crystal surface, which indicates the crucial role of water molecules in air on the phase transition dynamics. We foresee that this laser method can be a practical tool for monitoring spatiotemporal dynamics of phase transition.

Denoising coherent Doppler lidar data based on a U-Net convolutional neural network.

The coherent Doppler wind lidar (CDWL) has long been thought to be the most suitable technique for wind remote sensing in the atmospheric boundary layer (ABL) due to its compact size, robust performance, and low-cost properties. However, as the coherent lidar exploits the Mie scattering from aerosol particles, the signal intensity received by the lidar is highly affected by the concentration of aerosols. Unlike air molecules, the concentration of aerosol varies greatly with time and weather, and decreases dramatically with altitude. As a result, the performance of the coherent lidar fluctuates greatly with time, and the detection range is mostly confined within the planetary boundary layer. The original data collected by the lidar are first transformed into a spectrogram and then processed into radial wind velocities utilizing algorithms such as a spectral centroid. When the signal-to-noise ratio (SNR) is low, these classic algorithms fail to retrieve the wind speed stably. In this work, a radial wind velocity retrieving algorithm based on a trained convolutional neural network (CNN) U-Net is proposed for denoising and an accurate estimate of the Doppler shift in a low-SNR regime. The advantage of the CNN is first discussed qualitatively and then proved by means of a numerical simulation. Simulated spectrum data are used for U-Net training and testing, which show that the U-Net is not only more accurate than the spectral centroid but also achieves a further detection range. Finally, joint observation data from the lidar and radiosonde show excellent agreement, demonstrating that the U-Net-based retrieving algorithm has superior performance over the traditional spectral centroid method both in accuracy and detection range.

Self-Charging, Breathable, and Antibacterial Poly(lactic acid) Nanofibrous Air Filters by Surface Engineering of Ultrasmall Electroactive Nanohybrids.

Despite the great promise in the development of biodegradable and ecofriendly air filters by electrospinning of poly(lactic acid) (PLA) nanofibrous membranes (NFMs), the as-electrospun PLA nanofibers are generally characterized by poor electroactivity and smooth surface, challenging the exploitation of electrostatic adsorption and physical interception that are in need for efficient removal of pathogens and particulate matters (PMs). Herein, a combined "electrospinning-electrospray" strategy was disclosed to functionalize the PLA nanofibers by direct anchoring of highly dielectric BaTiO3@ZIF-8 nanohybrids (BTO@ZIF-8), conferring simultaneous promotion of surface roughness, electret properties (surface potential as high as 7.5 kV), and self-charging capability (∼190% increase in tribo-output voltage compared to that of pure PLA). Benefiting from the well-tailored morphology and increased electroactivity, the electrospun-electrosprayed PLA/BTO@ZIF-8 exhibited excellent PM-capturing performance (up to 96.54% for PM0.3 and 99.49% for PM2.5) while providing desirable air resistance (only 87 Pa at 32 L/min) due primarily to the slip flow of air molecules over the nanohybrid protrusions. This was accompanied by excellent antibacterial properties (99.9% inhibition against both Staphylococcus aureus and Escherichia coli), arising presumably from the synergistic effects of enhanced reactive oxygen species (ROS) generation, plentiful ion release, and surface charges. Our proposed strategy opens up pathways to afford exceptional combination of high-efficiency and low-resistance filtration, excellent antibacterial performance, and mechanical robustness without sacrificing the biodegradation profiles of PLA NFMs, holding potential implications for efficient and long-term healthcare.

Evolutions of streamer dynamics and discharge instabilities under repetitive pulses in humid air

The presence of water molecules in air introduces complexities to residual charge transports and energy relaxations that may provoke streamer discharge instabilities under repetitive pulses. Evolutions of pulse-periodic positive streamer dynamics were investigated in humid air. Pulse-sequence and temporally resolved diagnostics were implemented to capture discharge evolutions. The streamer development and evolutions of charged species in humid air are qualitatively analyzed based on a 2D–0D combined simulation. Evolution features of streamer behaviors in humid air include the faster filamentation of the primary streamer, pronounced propagation selectivity to previous secondary streamers, more branches of both primary and secondary streamers, and accelerated secondary streamer into stagnation. The repetitively pulsed breakdown is proceeded by the progressive axial prolongation of secondary streamers with bright heads and faint tails. Nonintuitively, the withstanding capability does not illustrate dramatic differences in dry air and humid air especially at high pulse repetition frequency. High-density residing hydrated ions with high electron bound energies (impeding streamer propagation) and the enhanced thermal release to cause higher reduced electric field (facilitating streamer propagation) may contrarily affect evolutions and discharge instability developments of positive streamer in humid air.

Vegetation Scattering Attenuation Characteristics of Terahertz Wave

A terahertz (THz) wave transmitted through vegetation experiences both absorption and scattering caused by the air molecules and leaves. This paper presents the scattering attenuation characteristics of vegetation in a THz range. The theoretical path loss model near the vegetation yields the average attenuation of THz waves in a mixed channel composed of air and vegetation leaves. Furthermore, a simplified model of the vegetation structure is obtained for generic vegetation types based on a variety of parameters, such as leaf size, distribution, and moisture content. Finally, based on specific vegetation species and different levels of air humidity, the attenuation characteristics under different conditions are calculated, and the influence of different model parameters on the attenuation characteristics is obtained.