Collision Gas Research Articles

Probing Contact Electrification between Gas and Solid Surface

Contact electrification exists everywhere and between every phase of matter. However, its mechanism still remains to be studied. The recent triboelectric nanogenerator serves as a probe and provides some new clues about the mechanism present in solid–solid, solid–liquid, and liquid–liquid contact electrification. The gas–solid model still remains to be exploited. Here, we investigated the contact electrification between gases and solids based on the single-electrode triboelectric nanogenerator. Our work shows that the amount of transferred charges between gas and solid particles increases with surface area, movement distance, and initial charges of particle increase. Furthermore, we find that the initial charges on the particle surface can attract more polar molecules and enhance gas collisions. Since ions in gas–solid contact are rare, we speculate that gas–solid contact electrification is mainly based on electron transfer. Further, we propose a theoretical model of gas–solid contact electrification involving the gas collision model and initial charges of the particle. Our study may have great significance to the gas–solid interface chemistry.

Measurement of stripping losses in the negative ion source SPIDER

The negative ion source SPIDER at Consorzio RFX (Italy) is a crucial experimental step towards the development of the Heating Neutral Beam (HNB) injectors for ITER. The goal of SPIDER is to operate and optimize a full-scale negative ion source in hydrogen and deuterium, with particles accelerated up to 100 keV. One of the processes having a considerable effect on the global efficiency of HNB systems is the partial neutralization of negative ions by gas collisions during their acceleration. This process is commonly referred to stripping losses and it can account up to 29% of the extracted current in a full-scale accelerator. The electrons generated by the neutralization of partially-accelerated negative ions can also contribute significantly to the total amount of heat deposited onto the acceleration grids. The investigation of stripping losses in SPIDER can provide useful methods to extrapolate and estimate also for the full scale HNB injector, called MITICA, currently under manufacturing. The purpose of this work is to develop a tool to estimate stripping losses in the accelerator of full scale HNB injectors based on beam emission spectra. The Beam Emission Spectroscopy (BES) technique has been employed to investigate stripping losses during the first SPIDER experimental campaign with caesium evaporation, characterized by larger extracted current densities compared to pre-caesium operations. Experimental data interpretation required synergy with beam models, necessary to account for the beam-gas interaction processes in the accelerator. In this work we describe the method of analysis and provide first estimates of stripping losses in SPIDER from data obtained during the first caesium operation campaign.

HiPIMS and RF magnetron sputtered Al0.5CoCrFeNi2Ti0.5 HEA thin-film coatings: Synthesis and characterization

High entropy alloy (HEA) thin-film coatings have gained popularity in surface engineering applications because of their excellent physical, mechanical, and electrochemical properties. Several factors affect thin-film coating density and microstructure, but most notably, the energy of the species impacting the substrate (adatoms); therefore, the deposition process is crucial. Hardness, wear resistance, toughness, corrosion-resistant, and high/low-temperature behavior can be significantly influenced by the microstructure of thin-film coatings. In radio frequency (RF) magnetron sputtering, plasma can be maintained throughout the chamber at lower pressure, so fewer ionized gas collisions occur, and coatings are deposited more efficiently. In comparison, the high-power impulse magnetron sputtering (HIPIMS) coating process produces much denser, harder, and smoother coatings than conventional thin-film deposition techniques. This study utilized RF magnetron sputtering and HiPIMS techniques to deposit Al0.5CoCrFeNi2Ti0.5 HEA thin-film coatings. The coatings presented an FCC structure with a (111) preferred orientation, and their surfaces changed from nodular to fine microstructures. The crystallite sizes and surface roughness decreased to 13.27 and 1.33 nm, respectively, based on FWHM and AFM analyses. The lower working pressures were beneficial for obtaining coatings with good properties. Furthermore, the Al0.5CoCrFeNi2Ti0.5 HEA thin-film coatings improved the corrosion resistance of the SS 304 substrate. In summary, HiPIMS and RF magnetron sputtering processes allow for better control of the properties of Al0.5CoCrFeNi2Ti0.5 thin-film coatings, enhancing their potential use in extreme environments.

Effect of discharge parameters on conductive behavior and characteristics of monopole plasma antenna

The plasma is used as radiating element in the reconfigurable antenna’s applications. For these applications, the plasma must behave like a conductor medium. In the first part of this paper, we study the conductive (or the dielectric) behavior of plasma medium for different discharge characteristics. The fluid model combined with the drift diffusion approach is used to calculate the plasma characteristics, such as the plasma density and the gas collision frequency. Then, the Drude model is used to determine the electrical parameters of the plasma. The results show that the conductive behavior depends on the operating frequency and the discharge characteristics. Indeed, the frequency bandwidth where the plasma medium behaves as conductor increases by increasing the electrode voltage and the plasma pressure. In the second part of this paper, we study the performance of the monopole plasma antenna. For this, a fluorescent tube filled with a low-pressure argon gas is used. The effect of different discharge characteristics on the reflection coefficient S11 is studied by the CST software.

Nb12 +-niobespherene: a full-metal hollow-cage cluster with superatomic stability and resistance to CO attack.

Why one chemical is more stable than another is not always easy to understand. A unified answer for metal clusters has led to the establishment of the superatom concept, which rationalizes the delocalization of electrons; however, cluster stability based on superatom theory has not been confirmed unambiguously for any metal other than the s- and p-blocks of the periodic table of elements. Here, we have prepared pure niobium clusters and observed their reactions with CO under sufficient gas collision conditions. We find prominent inertness of Nb12 +, which survives CO attack. Comprehensive theoretical calculation results reveal that the inertness of Nb12 + is associated with its cage structure and well-organized superatomic orbitals, giving rise to energetic superiority among the studied clusters. It is revealed that not only the 5s but also the 4d electrons of Nb delocalize in the cluster and significantly contribute to the superatomic state, resulting in reasonable cage aromaticity. This hollow-cage cluster, which we have called a 'niobespherene', provides a clue with regard to designing new materials of all-metal aromaticity and Nb-involved catalysts free of CO poisoning.

Evidence of Gas-Phase Attachment of Molecular Oxygen to Deprotonated Hydroquinone During Ion-Mobility Mass Spectrometry.

Gas-phase addition of dioxygen to certain ions is a well-known phenomenon in mass spectrometry. For this reaction to occur, the presence of a distonic radical site on the precursor ion is thought to be a prerequisite. Herein, we report that oxygen adduct formation can take place also with deprotonated hydroquinone, which in fact is an even-electron species without a radical site. When the product-ion spectrum of the m/z 109 ion, generated by electrospray ionization from a solution of hydroquinone in acetonitrile, was recorded under ion-mobility conditions, a new peak was observed at m/z 141. However, an analogous peak was not visible in the spectrum acquired under nonmobility conditions (i.e., without any gas introduced to the mobility cell). Presumably, traces of oxygen present in the collision gas instigate an ion-molecule reaction to produce an adduct of m/z 141, which upon activation results in CO and H2O loss to form a product ion of m/z 95. Isotope-labeling studies confirmed that one of the hydrogen atoms from the hydroxy group and another from the aromatic ring contribute to the water loss instigated from the m/z 141 adduct. Furthermore, computational methods indicated the three-dimensional structure of the ground-state deprotonated hydroquinone to be distinctly different from those of its 1,2- and 1,3-isomers. Calculations predicted that all atoms in the two m/z 109 ions generated from catechol and resorcinol lie on one plane. In contrast, the structure of the m/z 109 ion from hydroquinone was significantly different. Computations predicted that the hydrogen atom on the intact hydroxyl group of deprotonated hydroquinone protrudes out of plane from rest of the atoms. Consequently, the exposed OH group can interact with an incoming dioxygen molecule. Computations conducted at the CAM-B3LYP/6-311++g(2d,2p) level of theory detected a minimum energy crossing point (MECP) at -4.3 kJ mol-1 below the separated O2 + deprotonated hydroquinone triplet threshold. In contrast, similar calculations conducted for catechol and resorcinol yielded MECPs of +116.9 and +69.1 kJ mol-1, respectively, above the associated triplet thresholds. These results indicated that the curve crossing required to form singlet products upon reaction with triplet O2 is favorable in the case of hydroquinone and unfavorable in the cases of catechol and resorcinol. In practical terms, the selective oxygen addition appears to be a diagnostically useful reaction to differentiate hydroquinone from its ring isomers.

Collision-Induced C60 Rovibrational Relaxation Probed by State-Resolved Nonlinear Spectroscopy

Quantum state-resolved spectroscopy was recently achieved for C60 molecules when cooled by buffer gas collisions and probed with a midinfrared frequency comb. This rovibrational quantum state resolution for the largest molecule on record is facilitated by the remarkable symmetry and rigidity of C60, which also present new opportunities and challenges to explore energy transfer between quantum states in this many-atom system. Here we combine state-specific optical pumping, buffer gas collisions, and ultrasensitive intracavity nonlinear spectroscopy to initiate and probe the rotation-vibration energy transfer and relaxation. This approach provides the first detailed characterization of C60 collisional energy transfer for a variety of collision partners, and determines the rotational and vibrational inelastic collision cross sections. These results compare well with our theoretical modeling of the collisions, and establish a route towards quantum state control of a new class of unprecedentedly large molecules.

Identification of Oxindoleacetic Acid Conjugates in Quinoa (Chenopodium quinoa Willd.) Seeds by High-Resolution UHPLC-MS/MS.

Quinoa (Chenopodium quinoa Willd.) has a high nutritional value and it contains a high number and high amounts of specialized metabolites. These metabolites include, for example, phenolic acids, flavonoids, terpenoids and steroids. In addition, it is known to contain N-containing metabolites, such as betalains. Here, we report the presence and identification of 14 new oxindoleacetate conjugates in quinoa by high-resolution ultrahigh-performance liquid chromatography quadrupole-time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS/MS) and ultrahigh-resolution UHPLC-QOrbitrap-MS/MS. The oxindoleacetate conjugates were extracted from dried and ground quinoa seeds using either methanol/water or acetone/water (4:1, v/v) and were further concentrated into aqueous phase and analyzed by UHPLC with reverse-phase chromatography using acetonitrile and 0.1% aqueous formic acid as eluents. High-resolution hybrid LC-MS/MS techniques, including full scan MS with in-source collision, induced dissociation, and data dependent-MS2(TopN) with stepped normalized collision energies using N2 as collision gas and data-independent acquisition (MSE) using ramped collision energies and argon as collision gas enabled their analysis directly from the crude quinoa seed extract. The oxindoleacetate conjugates were found to be present in both conventional and organic farmed seeds. According to our best knowledge, this is the first time hydroxy-oxindoles have been reported in quinoa.

The Kinetic Monte Carlo Model of the Auroral Electron Precipitation into N2-O2 Planetary Atmospheres

Auroral events are the prominent manifestation of solar/stellar forcing on planetary atmospheres. They are closely related to the energy deposition by and evolution of planetary atmospheres, and their observations are widely used to analyze the composition, structure, and chemistry of the atmosphere under study, as well as energy fluxes of the precipitating particles that affect the atmosphere. A numerical kinetic Monte Carlo model had been developed, allowing us to study the processes of precipitation of high-energy auroral electrons into the N2-O2 atmospheres of the rocky planets in the Solar and exosolar planetary systems. This model describes on a molecular level the collisions of auroral electrons and atmospheric gas, taking into account the stochastic nature of collisional scattering at high kinetic energies. The current status of the kinetic model is illustrated in the applications to the auroral events on the Earth such as the production of suprathermal nitrogen atoms due to the electron impact dissociation of N2. It was found that electron impact dissociation of N2 can potentially be an important source of suprathermal N atoms in the auroral regions of the N2-O2 atmosphere of terrestrial-type planets. Such research will allow us to study the odd nitrogen chemistry as an atmospheric marker of the N2-O2 atmosphere of rocky exoplanets.

Sensitive liquid chromatography/tandem mass spectrometry method for the simultaneous determination of seventeen beta blockers

In recent years, examples of drugs responsible for acute drug intoxication in elderly people include benzodiazepines, phenobarbital, digitalis preparations, phenytoin, beta blockers or calcium antagonists, and antidepressants in Japan. Due to the diversity of underlying diseases, the reasons for this include increasing number of prescription medicines due to regular oral medicines themselves interacting, and age-related changes in drug metabolism. Beta blockers for clinical use are employed in the management of a range of disorders, including hypertension, heart failure, arrhythmias, migraine headache and tremor. Beta blockers are prescribed widely and also have a high frequency of accidental ingestion by the elderly people. Cardiovascular drugs (beta blockers) present more serious symptoms of intoxication than the underlying diseases themselves. The aim of this study is to develop and validate a sensitive liquid chromatography–tandem mass spectrometry (LC-MS/MS) with ESI method for the simultaneous determination of seventeen beta blockers (atenolol, carteolol, nadolol, pindolol, timolol, acebutolol, arotinolol, metoprolol, esmolol, celiprolol, labetalol, bisoprolol, propranolol, alprenolol, betaxolol, bevantolol and carvedilol). The extractions of beta blockers in human serum were performed by solid-phase extraction method using Oasis® PRiME HLB column (Waters). LC-MS/MS experiments were performed with a HPLC system, which consisted of Shimadzu LC-20AD pumps, a SIL-20AC autosampler and the 4000 QTRAP mass spectrometer (AB SCIEX). The chromatographic separation was performed on a Mightysil-RP-18 MS column (150 × 2.0-mm i.d., 5 μm). For the gradient elution, two solvents were used: (A) 10 mM acetic ammonium buffer and (B) acetonitrile. The flow rate was 0.20 mL/min and the column and autosampler were maintained at 37 and 4˚C, respectively. The settings of the turbo ion-spray were as follows; curtain gas, N2:40 psi, collision gas, N2:4 psi, collision energy: 27∼41 V, ion-spray voltage: 5500 V, ionization mode: ESI positive, source temperature: 600˚C. Separation and sensitivity for the detection of seventeen beta blockers by LC-MS/MS were sufficient and the precursor [M + H]+ ion was detected in the mass spectrum for each drug. This method had a chromatographic total run time of 15 min. The calibration curves were linear over the concentration range of 20–400 ng/mL for seventeen beta blockers (r = 0.9686∼0.9997). The extraction yields of human serum sample with Oasis® PRiME HLB column were ranged from 66.1 to 93.5%, the precision within 0.07 CV values were acceptable of this method. But the extraction yields of bevantlol (37.5%) and carvedilol (26.2%) were low. Currently, we are experimenting to improve the extraction yields of bevantolol and carvedilol. Phyo Lwin EM, et al (2017, Bioanalysis.) developed a method for the determination of atenolol in human plasma and milk sample by LC-MS/MS. The limits of detection (LOD) and quantification (LOQ) were in the range 1.0 ng/mL and 5.0 ng/mL for atenolol. Our LC-MS/MS with ESI method was able to measure compounds at approximately the same concentrations as the analytical methods of Phyo Lwin EM, et al. In our experiments, LOD and LOQ in the range 0.0034–1.6 ng/mL and were 20 ng/mL for seventeen beta blockers. The presently established method is very useful for simultaneous measurements of beta blockers in human serum by LC-MS/MS in clinical and forensic investigations.

Per capita wealth in cities and regions fitted to Pareto, stretched exponential and econophysics Boltzmann–Gibbs distributions

From the years 2001 to 2017, per capita nominal and real (adjusted to inflation) GDP at purchasing power parity (PCGDP-PPP) distributions for cities and regions are fitted to various functions. For most years and regions, real PCGDP-PPP data are very well adjusted to the one-parameter Boltzmann–Gibbs distribution (BGD), in accordance with the exponential behavior predicted by the simple econophysics analogy between conserved money in economic trade and energy in elastic collisions in gases. Overall, fittings are better for large regions in recent years, which may reflect an increasing economic globalization in time. Cities, small regions and large regions values are well fitted by stretched exponential distributions.

Spherical accretion of collisional gas in modified gravity I: self-similar solutions and a new cosmological hydrodynamical code

ABSTRACT The spherical collapse scenario has great importance in cosmology since it captures several crucial aspects of structure formation. The presence of self-similar solutions in the Einstein-de Sitter (EdS) model greatly simplifies its analysis, making it a powerful tool to gain valuable insights into the real and more complicated physical processes involved in galaxy formation. While there has been a large body of research to incorporate various additional physical processes into spherical collapse, the effect of modified gravity (MG) models, which are popular alternatives to the Λ cold dark matter paradigm to explain the cosmic acceleration, is still not well understood in this scenario. In this paper, we study the spherical accretion of collisional gas in a particular MG model, which is a rare case that also admits self-similar solutions. The model displays interesting behaviours caused by the enhanced gravity and a screening mechanism. Despite the strong effects of MG, we find that its self-similar solution agrees well with that of the EdS model. These results are used to assess a new cosmological hydrodynamical code for spherical collapse simulations introduced here, which is based on the hyperbolic partial differential equation engine ExaHyPE 2. Its good agreement with the theoretical predictions confirms the reliability of this code in modelling astrophysical processes in spherical collapse. We will use this code to study the evolution of gas in more realistic MG models in future work.

SDSS-IV MaNGA: global properties of kinematically misaligned galaxies

ABSTRACT We select 456 gas–star kinematically misaligned galaxies from the internal Product Launch-10 of MaNGA survey, including 74 star-forming (SF), 136 green-valley (GV), and 206 quiescent (QS) galaxies. We find that the distributions of difference between gas and star position angles for galaxies have three local peaks at ∼0°, 90°, and 180°. The fraction of misaligned galaxies peaks at log (M*/M⊙) ∼ 10.5 and declines to both low- and high-mass end. This fraction decreases monotonically with increasing star formation rate and specific star formation rate. We compare the global parameters including gas kinematic asymmetry Vasym, H i detection rate and mass fraction of molecular gas, effective radius Re, Sérsic index n as well as spin parameter $\lambda _{R_e}$ between misaligned galaxies and their control samples. We find that the misaligned galaxies have lower H i detection rate and molecular gas mass fraction, smaller size, higher Sérsic index, and lower spin parameters than their control samples. The SF and GV misaligned galaxies are more asymmetric in gas velocity fields than their controls. These pieces of observational evidence point to the gas accretion scenario followed by angular momentum redistribution from gas–gas collision, leading to gas inflow and central star formation for the SF and GV misaligned galaxies. We propose three possible origins of the misaligned QS galaxies: (1) external gas accretion, (2) merger, and (3) GV misaligned galaxies evolve into QS galaxies.

Origin of viscosity at individual particle level in Yukawa liquids

The transition of the viscosity $\ensuremath{\eta}$ from a collisional gas through a minimum value to a correlated liquid is investigated using computer simulations with the Green-Kubo relation. It is discovered that, as the temperature varies, the transition of $\ensuremath{\eta}$ is well described by the unity ratio of the instantaneous transverse sound speed ${C}_{T}$ to the average particle speed ${\overline{v}}_{p}$. While ${C}_{T}/{\overline{v}}_{p}<1, \ensuremath{\eta}$ increases with the temperature, since in this regime the viscosity is dominated by the gaslike individual dynamics. However, when ${C}_{T}/{\overline{v}}_{p}>1$ where the cooperative dynamics dominates, the fundamental origin of viscosity of liquids is found to be just losing or gaining neighbors for individual particles, so that the viscosity of a typical liquid reasonably decreases with the temperature. Our results reveal that the viscosity transition point of ${C}_{T}/{\overline{v}}_{p}=1$ is just $\ensuremath{\approx}20$ times the corresponding melting point for both two-dimensional and three-dimensional Yukawa liquids with various screening parameters, which probably can be used as a new criterion to distinguish the strong and weak couplings in plasma physics.

Застосування числових методів газодинамічних розрахунків в задачах обтікання перешкод розрідженим струминним потоком

The development of competitive space hardware calls for continuing improvements in the accuracy of simulation of gas-dynamic processes in the space vehicle vicinity. This may contribute to extending the active life of spacecraft, thus improving the economic efficiency of space activities. In particular, quite a topical problem is the simulation of the interaction of rarefied jets from the propulsion system of a spacecraft with its individual components. To solve this problem in the case of a rather high surrounding vacuum, use is made of the molecular-kinetic concept of the gas structure based on the Boltzmann equation. The aim of this paper is to overview existing methods of simulation of gas-dynamic processes near spacecraft in a rarefied gas flow with account for propulsion system jets and to choose the most promising approaches to the solution of this problem. Among the methods considered, several main lines are set off: approximate, analytical, and numerical methods. Approximate methods use physical models of jet flow, approximation of numerical results, or a combination of both approaches. Analytical methods are based on essentially simplified assumptions and are intended for a very narrow class of problems. Numerical methods are the most universal tool of theoretical study. At the same time, each numerical method has a range of application of its own. At present, the most used and promising methods are statistical simulation methods: the direct simulation Monte Carlo method (DSMCM) and the test particle method (TPM). The former splits the continuous process of molecule motion and collisions in a rarefied gas into two successive independent stages (free-molecular transfer and relaxation) at each small time step. The simulation is done by time steps and in fact reproduces a nonstationary process. The latter, the TPM, consist in a statistical successive simulation of the wandering of test particles (molecules) on the background of field ones about the cells of the computational grid. Test particles, which move within the cells of the computational area, periodically collide with the obstacle in the flow and field particles, and in doing so they gradually change both their velocity and the field characteristics. For both statistical approaches, the simulation accuracy, as can be expected, is inversely proportional to the square root of the number of tests: the number of time steps and modeling particles for the DSMCM and the number of successively simulated test particle trajectories for the TPM. This may greatly affect the possibility of attaining a desired accuracy.

Narrow-line imaging of single strontium atoms in shallow optical tweezers

Single strontium atoms held in optical tweezers have so far only been imaged using the broad ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{1}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition. For Yb, use of the narrow (183-kHz wide) ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{3}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition for simultaneous imaging and cooling has been demonstrated in tweezers with a magic wavelength for the imaging transition. We demonstrate high-fidelity imaging of single Sr atoms using its even narrower (7.4-kHz wide) ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{3}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition. The atoms are trapped in nonmagic-wavelength tweezers. We detect the photons scattered during Sisyphus cooling, thus keeping the atoms near the motional ground state of the tweezer throughout imaging. The fidelity of detection is 0.9991(4) with a survival probability of 0.97(2). An atom in a tweezer can be held under imaging conditions for 79(3) seconds allowing for hundreds of images to be taken, limited mainly by background gas collisions. The use of a fully closed (cycling) transition for imaging will provide a useful tool for state specific detection. We detect atoms in an array of 36 tweezers with 813.4-nm light and trap depths of 135(20) $\ensuremath{\mu}$K. This trap depth is three times shallower than typically used for imaging on the broad ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{1}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition. Narrow-line imaging opens the possibility to even further reduce this trap depth, as long as all trap frequencies are kept larger than the imaging transition linewidth. Imaging using a narrow-linewidth transition in a nonmagic-wavelength tweezer also allows for selective imaging of a given tweezer. As a demonstration, we selectively image (hide) a single tweezer from the array. This provides a useful tool for quantum error correction protocols.

The dynamics of ions on phased radio-frequency carpets in high pressure gases and application for barium tagging in xenon gas time projection chambers

Radio-frequency (RF) carpets with ultra-fine pitches are examined for ion transport in gases at atmospheric pressures and above. We develop new analytic and computational methods for modeling RF ion transport at densities where dynamics are strongly influenced by buffer gas collisions. An analytic description of levitating and sweeping forces from phased arrays is obtained, then thermodynamic and kinetic principles are used to calculate ion loss rates in the presence of collisions. This methodology is validated against detailed microscopic SIMION simulations. We then explore a parameter space of special interest for neutrinoless double beta decay experiments: transport of barium ions in xenon at pressures from 1 to 10 bar. Our computations account for molecular ion formation and pressure dependent mobility as well as finite temperature effects. We discuss the challenges associated with achieving suitable operating conditions, which lie beyond the capabilities of existing devices, using presently available or near-future manufacturing techniques.

Evaluation of collision/reaction gases in single-particle ICP-MS for sizing selenium nanoparticles and assessment of their antibacterial activity

Selenium nanoparticles (SeNPs) have recently attracted attention because they combine the benefits of Se and lower toxicity compared to other chemical forms of this element. In this study, SeNPs were synthesized by a green method using ascorbic acid as the reducing agent and polyvinyl alcohol as stabilizer. The nanoparticles were widely characterized. To determine the total concentration of Se by ICP-MS, several isotopes and the use of He as collision gas were evaluated, which was effective in minimizing interferences. A method for sizing SeNPs by single particle ICP-MS (SP-ICP-MS) was developed. For this purpose, He and H2 were evaluated as collision/reaction gases, and the second one showed promising results, providing an average diameter of 48 nm for the SeNPs. These results agree with those obtained by TEM (50.1 nm). Therefore, the SP-ICP-MS can be implemented for characterizing SeNPs in terms of size and size distribution, being an important analytical tool for Se and other widely studied nanoparticles (e.g. Ag, Au, Ce, Cu, Fe, Zn). Finally, the antibacterial activity of SeNPs was assessed. The SeNPs showed bacteriostatic activity against three strains of Gram-positive bacteria and were particularly efficient in inhibiting the growth E. faecalis even at very low concentrations (MIC < 1.4 mg l−1). In addition, a bactericidal activity of SeNPs against S. aureus was observed. These nanoparticles may have potential application in pharmaceutical industry, biomedicine and agriculture.

Three-dimensional geometry and dust/gas ratios in massive star-forming regions over the entire LMC as revealed by the IRSF/SIRIUS survey

Abstract We derive the entire dust extinction (AV) map for the Large Magellanic Cloud (LMC) estimated from the color excess at near-infrared wavelengths. Using the percentile method we recently adopted to evaluate AV distribution along the line of sight, we derive three-dimensional (3D) AV maps of the three massive star-forming regions of N44, N79, and N11 based on the IRSF/SIRIUS point source catalog. The 3D AV maps are compared with the hydrogen column densities N(H) of three different velocity components where one is of the LMC disk velocity and the other two are of velocities lower than the disk velocity. As a result, we obtain a 3D dust geometry suggesting that gas collision is ongoing between the different velocity components. We also find differences in the timing of the gas collision between the massive star-forming regions, which indicates that the gas collision in N44, N79, and N11 occurred later than that in 30 Doradus. In addition, a difference of a factor of two in AV/N(H) is found between the velocity components for N44, while a significant difference is not found for N79 and N11. From the 3D geometry and AV/N(H) in each star-forming region, we suggest that the massive star formation in N44 was induced by an external trigger of tidal interaction between the LMC and the Small Magellanic Cloud, while that in N79 and N11 is likely to have been induced by internal triggers such as gas converging from the galactic spiral arm and expansion of a supershell, although the possibility of tidal interaction cannot be ruled out.

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis: A Strategy for Ammonia Synthesis under Mild Conditions

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis: A Strategy for Ammonia Synthesis under Mild Conditions