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Although it plays a critical role in the photophysics and catalysis of lanthanides, spin–orbit coupling of electrons on individual lanthanide atoms in small clusters is not well understood. The major objective of this work is to probe such coupling of the praseodymium (Pr) 4f and 6s electrons in Pr2O2 and Pr2O2+. The approach combines mass-analyzed threshold ionization spectroscopy and spin–orbit multiconfiguration second-order quasi-degenerate perturbation theory. The energies of six ionization transitions are precisely measured; the adiabatic ionization energy of the neutral cluster is 38 045 (5) cm−1. Most of the electronic states involved in these transitions are identified as spin–orbit coupled states consisting of two or more electron spins. The electron configurations of these states are 4f46s2 for the neutral cluster and 4f46s for the singly charged cation, both in planar rhombus-type structures. The spin–orbit splitting due to the coupling of the electrons on the separate Pr atoms is on the order of hundreds of wavenumbers. [ABSTRACT FROM AUTHOR]

We demonstrate similarity rules for inductively coupled plasmas with thermohydrodynamic coupling effects using two-dimensional fluid simulations and theoretical analyses of the gas flow and heat transfer equations. The results confirm the validity of conventional similarity laws, e.g., the similarity relation for electron density, which can be violated by the nonlinear gas heating effects from exothermic and endothermic reactions. The nonlinear gas heating can obviously perturb the invariance of spatial distributions of the gas flow velocity, resulting in the electron density decreasing nonproportionally with different scaling factors. Adding an external heat source can mitigate the violation of the gas temperature scaling law, thus maintaining the validity of similarity relations to some extent. In addition, two kinds of scaling relations for excited-state argon atoms are identified with and without the consideration of nonlinear collisions. [ABSTRACT FROM AUTHOR]

The thermodynamic properties of boron nitride under extreme pressures and temperatures are of great interest and importance for materials science and inertial confinement fusion physics, but they are poorly understood owing to the challenges of performing experiments and realizing ab initio calculations. Here, we report the first shock Hugoniot data on hexagonal boron nitride at pressures of 5–16 Mbar, using hohlraum-driven shock waves at the SGIII-p laser facility in China. Our density functional theory molecular dynamics calculations closely match experimental data, validating the equations of state for modeling the shock response of boron nitride and filling a crucial gap in the knowledge of boron nitride properties in the region of multi-Mbar pressures and eV temperatures. The results presented here provide fundamental insights into boron nitride under the extreme conditions relevant to inertial confinement fusion, hydrogen–boron fusion, and high-energy-density physics. [ABSTRACT FROM AUTHOR]

The Kirkpatrick–Baez (KB) microscope is an effective instrument for x-ray imaging of hot spot. However, the non-uniform distribution of response efficiency in the field of view is a drawback of the KB microscope. A more accurate hot spot image requires the correction of the measured image by combining the hot spot position and the response efficiency distribution. Here, we describe a method to locate the position of the hot spot in the field of view during hot spot imaging with a KB microscope. The position of the hot spot in the field of view can be obtained by measuring the grazing incidence angle change during hot spot imaging. In the experiment of hot spot self-emission imaging with a four-channel KB microscope, the location of the hot spot with an accuracy of 15 μm was realized, and the intensity corrected hot spot image was obtained. This will solve the problem of the non-uniform distribution of the response efficiency of the KB microscope and enable quantitative measurement of hot spot radiation intensity. [ABSTRACT FROM AUTHOR]

In this paper, the ignition process of the plasma scalpel is characterized by means of numerical simulation, shadowgraphy, and voltage–current measurements. The ignition process involves two phases: the pre-breakdown phase and the breakdown phase. Our study shows that in the pre-breakdown phase, the vapor layer is first generated around the corners of the active electrode and then gradually extends to cover the entire active electrode. Once the active electrode is fully covered by the vapor layer, the electric field reaches a maximum of 7.3 × 106 V m−1, which can cause discharge in the vapor layer. At this moment, the thickness of the vapor layer is approximately 100 μm. In the breakdown phase, the maximum electron density reaches 1018–1019 m−3. The plasma dissipates about 60% of the total power which is up to 125 W, thus enabling efficient cutting. In addition, we simulate the discharge characteristics of cutting various biological tissues. The results show that under the same voltage level, the higher the conductivity of biological tissues, the greater the discharge current. The biological tissues act as ballast resistors in equivalent circuits. [ABSTRACT FROM AUTHOR]

The main focus of this paper is to discover the link between flame macrostructure and thermoacoustic instability in a centrally staged swirl burner. In practical combustors, the flow rate in the pilot stage is much smaller than that in the main stage. However, the modification in the pilot stage could alter the flame macrostructure while maintaining a similar total flow rate. Therefore, the thermoacoustic instability was examined at different flame macrostructures by varying the pilot stage equivalence ratio under identical main stage inlet conditions. High-frequency planar laser measurements and chemiluminescence measurement were conducted to enhance spatial and temporal accuracy, providing a more comprehensive understanding of thermoacoustic instability. Two different flame macrostructures, S-type and I-type flames, were identified based on the preheating zone distribution. They exhibit distinct thermoacoustic instabilities, with the I-type flames demonstrating more intense instability than S-type flames. The results indicate that the variation of flame macrostructure influences the coupling of flame heat release and flow field. Specifically, the preheating zone and heat release of I-type flames exhibit greater sensitivity to flow field fluctuations, resulting in a more intense and complex fluctuation of the flame. This discrepancy leads to variations in thermoacoustic instability intensity, as well as the changes in the phase coupling between heat release and acoustic pressure, which in turn impact the total Rayleigh index. Meanwhile, significant differences exist in the distribution pattern and range of flow field fluctuations between I-type and S-type flames. [ABSTRACT FROM AUTHOR]

In recent years, there have been reports of gas leakage accidents during the transportation of gas tankers in tunnels, potentially leading to destructive explosions. However, the overall distribution of gas concentration in the entire tunnel has not been experimentally investigated. This study presents a series of brine-water experiments to explore the characteristics of buoyant gas flow in tunnel leakage accidents. The gas distribution is categorized into a stably stratified longitudinal current and a source region. Gas concentration in the tunnel is correlated with the dimensionless reduced gravity, which increases with the source buoyancy flux but decreases with the source release velocity. A model is proposed to estimate the maximum gas concentration of the longitudinal current. The spatial range of the explosive region is influenced by the source buoyancy flux and the leakage velocity. However, the propagation velocity of the longitudinal current is primarily controlled by the source buoyancy flux, with the source momentum having a negligible effect. The thickness of the longitudinal gas flow, δ, linearly decreases from the source region to the tunnel ends. A dimensionless parameter, λ, is introduced to characterize δ. When λ < 1.25, δ rapidly increases with λ and then remains approximately constant when λ exceeds 1.25. This study contributes to a better understanding of buoyant gas flow in tunnel leakage accidents. [ABSTRACT FROM AUTHOR]

The precise ionization energy of praseodymium oxide (PrO) seeded in supersonic molecular beams is measured with mass-analyzed threshold ionization (MATI) spectroscopy. A total of 33 spin–orbit (SO) states of PrO and 23 SO states of PrO+ are predicted by second-order multiconfigurational quasi-degenerate perturbation (MCQDPT2) theory. Electronic transitions from four low-energy SO levels of the neutral molecule to the ground state of the singly charged cation are identified by combining the MATI spectroscopic measurements with the MCQDPT2 calculations. The precise ionization energy is used to reassess the ionization energies and the reaction enthalpies of the Pr + O → PrO+ + e− chemi-ionization reaction reported in the literature. An empirical formula that uses atomic electronic parameters is proposed to predict the ionization energies of lanthanide monoxides, and the empirical calculations match well with available precise experimental measurements. [ABSTRACT FROM AUTHOR]

In an experiment performed on the Shenguang-III prototype laser facility, collective Thomson scattering (TS) is used to study the spatial growth of stimulated Brillouin scattering (SBS) in a gas-filled Hohlraum by detecting the SBS-driven ion acoustic wave. High-quality time-resolved SBS and TS spectra are obtained simultaneously in the experiment, and these are analyzed by a steady-state code based on the ray-tracing model. The analysis indicates that ion–ion collisions may play an important role in suppressing SBS growth in the Au plasma; as a result, the SBS excited in the filled gas region is dominant. In the early phase of the laser pulse, SBS originates primarily from the high-density plasma at the edges of the interaction beam channel, which is piled up by the heating of the interaction beam. Throughout the duration of the laser pulse, the presence of the TS probe beam might mitigate SBS by perturbing the density distribution around the region overlapping with the interaction beam. [ABSTRACT FROM AUTHOR]

The structural and bonding properties of the Pt2C2n− (n = 1–3) complexes have been investigated by mass-selected photoelectron velocity-map imaging spectroscopy with quantum chemical calculations. The adiabatic detachment energies and vertical detachment energies of Pt2C2n− have been obtained from the measured photoelectron imaging spectra. Theoretical results indicate that the lowest-energy isomers of Pt2C2n− (n = 1–3) possess linear chain-shaped configurations. The binding motif in the most stable isomer of Pt2C2− has a linear cumulenic structure with a Pt=C=C=Pt configuration, and the structural characteristic persists up to all the lowest-energy isomers of the Pt2C4− and Pt2C6− anions. The chemical bonding analyses indicate that the Pt2C2n− (n = 1–3) complexes have multicenter two-electron characteristics. [ABSTRACT FROM AUTHOR]

Vibronic spectra of lutetium oxide (LuO) seeded in supersonic molecule beams are investigated with mass-analyzed threshold ionization (MATI) spectroscopy and second-order multiconfigurational quasi-degenerate perturbation (MCQDPT2) theory. Six states of LuO and four states of LuO+ are located by the MCQDPT2 calculations, and an a3Π(LuO+) ← C2Σ+ (LuΟ) transition is observed by the MATI measurement. The vibronic spectra show abnormal vibrational intervals for both the neural and cation excited states, and the abnormality is attributed to vibrational perturbations induced by interactions with neighboring states. [ABSTRACT FROM AUTHOR]

Four-dimensional flow magnetic resonance imaging (4D flow MRI) offers a powerful tool for visualizing fluid flows, critical for both diagnosing cardiovascular diseases and analyzing engineering fluid dynamics. Despite its potential in medical research, the clinical applicability of 4D flow MRI often faces challenges due to inherent noise. To mitigate this, we introduce the split-and-overlap singular value decomposition (SOSVD) filter, a distinctive noise reduction approach. Unlike traditional singular value decomposition methods, the SOSVD filter partitions the primary data matrix into overlapping subdomains and then applies singular value decomposition to each subdomain, preserving only the dominant mode for noise attenuation. Evaluations on simulated and experimental flow data within a square duct revealed a significant decrease in root mean square noise metrics. Moreover, when applied to in vivo aortic data, the SOSVD filter enhanced various flow determinants, including divergence, velocity gradients, streamlines, and velocity coherence. Thus, the SOSVD method presents a promising avenue for augmenting noise reduction in 4D flow MRI, potentially elevating diagnostic accuracy and enriching cardiovascular disease research. [ABSTRACT FROM AUTHOR]

Metal-mediated N–H and C–H bond activation of aliphatic amines is an effective strategy for synthesizing biologically important molecules. Ln (Ln = La and Ce) atom reactions with dimethylamine are carried out in a pulsed-laser vaporization supersonic molecular beam source. A series of dehydrogenation species are observed with time-of-flight mass spectrometry, and the dehydrogenated Ln-containing species in the formula Ln(CH2NCH3) are characterized by single-photon mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical calculations. The theoretical calculations include density functional theory for both Ln species and multiconfiguration self-consistent field and quasi-degenerate perturbation theory for the Ce species. The MATI spectrum of La(CH2NCH3) consists of a single vibronic band system, which is assigned to the ionization of the doublet ground state of N-methyl-lanthanaaziridine. The MATI spectrum of Ce(CH2NCH3) displays two vibronic band systems, which are attributed to the ionization of two-pair lowest-energy spin–orbit coupling states of N-methyl-ceraaziridine. Both metallaaziridines are three-membered metallacycles and formed by the thermodynamically and kinetically favorable concerted dehydrogenation of the amino group and one of the methyl groups. [ABSTRACT FROM AUTHOR]

We demonstrate similarity-based scaling networks for capacitive radio frequency (RF) plasmas, which extensively correlate discharge characteristics under varied conditions, incorporating the transition from original to similarity states. Based on fully kinetic particle-in-cell simulations, similar RF discharges in argon are demonstrated with three external control parameters (gas pressure, gap distance, and driving frequency) simultaneously tuned. A complete set of scaling pathways regarding fundamental discharge parameters is obtained, from which each plasma state finds its neighboring node with only one control parameter tuned. The results from this study provide a promising strategy for plasma multi-parameter mapping, enabling effective cross-comparisons, prediction, and manipulation of RF discharge plasmas. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic perovskite (HOIP) materials have attracted significant attention in photovoltaics, light emission, photodetection, etc. Based on the prototype metal halide perovskite crystal, there is a huge space for tuning the composition and crystal structure of this material, which would provide great potential to render multiple physical properties beyond the ongoing emphasis on the optoelectronic property. Recently, the two-dimensional (2D) HOIPs have emerged as a potential candidate for a new class of ferroelectrics with high Curie temperature and spontaneous polarization. Room-temperature solution-processability further makes HOIP a promising alternative to traditional oxide ferroelectrics such as BaTiO3 and PbTiO3. In this perspective, we focus on the molecular aspects of 2D HOIPs, their correlation with macroscopic properties, as well as the material design rules assisted by advanced simulation tools (e.g., machine learning and atomistic modeling techniques). The perspective provides a comprehensive discussion on the structural origin of ferroelectricity, current progress in the design of new materials, and potential opportunities and challenges with emerging materials. We expect that this perspective will provide inspiration for innovation in 2D HOIP ferroelectrics. [ABSTRACT FROM AUTHOR]

Upconverting nanoparticles (UCNPs) composed of NaYF4 and doped with photoactive Yb3+ and Er3+ (NaYF4:Yb/Er) are highly desirable for many biological applications, but obtaining stable dispersions of UCNPs is challenging. Traditional synthetic methods often use complicated synthetic steps, produce toxic side products, and require post modifications to make UCNPs more dispersible in aqueous solutions. In this study, we demonstrate that laser ablation in liquid (LAL) is a novel approach to synthesize water-dispersible and -stable UCNPs with advantages of particle-size tuning, in situ coating of UCNPs with capping agents, no use of toxic or high boiling point solvents, and short reaction times. NaYF4:Yb/Er UCNPs were produced through LAL of annealed targets using water as the liquid, and their compositions and properties were investigated at a laser fluence of 0.57 J cm−2–6.22 J cm−2 by direct capping with citric acid and ethylene glycol and by comparing with the UCNPs prepared from the traditional hydrothermal method. Low laser fluences produced polydisperse particles consisting of no photoactive species through a thermal evaporation mechanism, while high laser fluences generated UCNPs with more uniform morphologies and compositions similar to the target material by an explosive ejection mechanism. The inclusion of capping agents during LAL allowed for direct coating of the UCNP surface without the need of post modifications, and the concentrations of capping agents affected the UCNP photoluminescence lifetimes. As compared to the hydrothermal method, the LAL-prepared samples showed better size control and no degradation of the capping agents. [ABSTRACT FROM AUTHOR]

Ln (Ln = La and Ce) atom reactions with methylamine are carried out in a pulsed-laser vaporization supersonic molecular beam source. A series of dehydrogenation species are observed with time-of-flight mass spectrometry, and the dehydrogenated Ln-containing species in the formula Ln(NCH3) are characterized by mass-analyzed threshold ionization (MATI) spectroscopy and density functional theory and multiconfiguration spin–orbit coupling computations. The MATI spectrum of La(NCH3) consists of two vibronic band systems that are assigned to the ionization of the 2A1 ground state of the C3v isomer La(N–CH3) and the 2A′ ground state of the Cs isomer La(NH–CH2). The MATI spectrum of Ce(NCH3) also displays two band systems, which are attributed to the ionization of the low-energy spin–orbit coupling states of the C3v isomer Ce(N–CH3). Ln(N–CH3) is formed by the concerted dehydrogenation of the amino group, while La(NH–CH2) is formed by the dehydrogenation of both amino and methyl groups. Ce(NH–CH2) is presumably formed in the reaction based on the computational predictions but not observed by the spectroscopic measurements. [ABSTRACT FROM AUTHOR]

A Ce atom reaction with propene is carried out in a pulsed laser vaporization molecule beam source. Several Ce–hydrocarbon species formed by the C—H and C—C bond activation of propene are observed by time-of-flight mass spectrometry, and Ce(C3Hn) (n = 4 and 6) are characterized by mass-analyzed threshold ionization (MATI) spectroscopy and density functional theory, multiconfiguration, and relativistic quantum chemical calculations. The MATI spectrum of each species consists of two vibronic band systems, each with several vibronic bands. Ce(C3H6) is identified as an inserted species with Ce inserting into an allylic C—H bond of propene and Ce(C3H4) as a metallocycle through 1,2-vinylic dehydrogenation. Both species have a Cs structure with the Ce 4f16s1 ground valence electron configuration in the neutral molecule and the Ce 4f1 configuration in the singly charged ion. The two vibronic band systems observed for each species are attributed to the ionization of two pairs of the lowest spin–orbit coupled states with each pair being nearly degenerate. [ABSTRACT FROM AUTHOR]

Resonance mechanisms have been found to be essential for the generation of high-density rf plasmas at low pressures, in which electrons can be continuously accelerated through multiple interactions with the oscillating rf sheaths. In this work, we report the scale-invariant resonance mechanisms, such as bounce resonance heating and plasma series resonance, in low-pressure capacitive rf plasmas in the presence of an external magnetic field. The generation conditions for the resonance mechanisms are determined via fully kinetic simulations. It is found that the resonance dynamical properties of single-frequency plasmas (e.g., a double-peak electron density vs magnetic field curve) can be exactly replicated at different scales when three combined control parameters, i.e., the reduced gap distance pd (pressure × distance), reduced driving frequency f/p (frequency divided by pressure), and reduced magnetic field B/p (magnetic field divided by pressure), are kept constant. The similarity relations for the electron density and electron power absorption in magnetized rf plasmas are numerically confirmed. Furthermore, the similarity and scale-invariant resonance characteristics are elucidated through the scaling of the Boltzmann equation with collisional terms for weakly ionized rf plasmas with a magnetic field, which is proven to be theoretically exact. [ABSTRACT FROM AUTHOR]

Both direct and indirect drive concepts of inertial confinement fusion rely on targets with cryogenic thermonuclear fuel shells for ignition. Experiments on the Shenguang-III prototype laser facility using laser-driven gas-filled hohlraums show distinct differences between cryogenic (20 K) and warm hohlraums. Although the measured x-ray flux in the photon range from 1.6 to 4.4 keV (Au M-band) is identical between cryogenic and warm hohlraums, the cryogenic hohlraum has a much slower rate of rise and is 20% lower in peak intensity of x-ray flux in the photon range from 0.1 to 4 keV. The reasons for this drive deficit between cryogenic and warm hohlraums are investigated using a similar series of hohlraum experiments. The experiments employ three types of hohlraums to distinguish the effect of a shroud window membrane and condensates. Warm hohlraums with a shroud window membrane replicate the slower rate of rise of radiation flux of cryogenic targets. When the shroud window is present, the measured x-ray flux in the hohlraum shows a drive deficit that decreases with time. However, the measured deficit increases as the viewing angle increases. All of these results indicate that the portion of the shroud not illuminated by the lasers absorbs the outgoing x-ray flux from the hohlraum. [ABSTRACT FROM AUTHOR]

There are several methods for treating aortic stenosis including transcatheter valve implantation (TAVI) and surgical aortic valve replacement. Among these, TAVI is highly recommended for elderly patients with high surgical risk or a life expectancy of less than 10 yr. However, recent research findings indicate that thrombosis after TAVI leads to the malfunction of TAVI leaflets, which increases the risk of stroke and heart attack. Since the mechanism of thrombus formation is unclear, this study aimed to investigate the sinus hemodynamics after TAVI in different configurations using particle image velocimetry. The results showed that compared with SAV, the TAV resulted in a relatively low velocity at the sinus owing to the native leaflet and skirt of the TAV. The native leaflet length, covering over 75% of TAV, significantly increased the flow stasis and particle residence. In addition, a larger sinus diameter corresponded to a larger stasis area of the same length as that of the native leaflet. According to this study, patients with long native leaflets in their aortic sinus are at a higher risk of developing thrombosis and may require a higher deployment during treatment. [ABSTRACT FROM AUTHOR]

Ce atom reactions with ethylene, 2-butene, and isobutene are carried out in a pulsed laser vaporization molecule beam source. Ce-containing species are observed with time-of-flight mass spectrometry, and Ce(C4H6) is characterized with mass-analyzed threshold ionization (MATI) spectroscopy and relativistic quantum chemical calculations. Two structural isomers are identified for Ce(C4H6): one is the tetrahedronlike Ce[C(CH2)3] in C3v symmetry and the other is the five-membered metallocyclic Ce(CH2CHCHCH2) in Cs. The MATI spectrum of the C3v isomer exhibits two vibronic band systems separated by 88 cm−1, while that of the Cs isomer displays three split by 60 and 101 cm−1. The multiple band systems are attributed to spin-orbit splitting and vibronic transitions involving metal-hydrocarbon and hydrocarbon-based vibrations. The splitting in the C3v isomer arises from interactions of two triplet and two singlet states at the lowest energies, while each splitting in the Cs isomer involves two triplets and a singlet. Although the Ce atom has ground electron configuration 4f15d16s2, Ce valence electron configurations in both isomers are 4f16s1 in the neutral ground state and 4f1 in the ion. The remaining Ce 5d electrons in the isolated atom are spin paired in molecular orbitals that are a bonding combination between Ce 5dπ and hydrocarbon π* orbitals. [ABSTRACT FROM AUTHOR]

Although lithium-sulfur (Li-S) batteries are widely regarded as one of the most promising next-generation high energy density storage systems, their large-scale applications are seriously impeded by rapid capacity fading and poor Coulombic efficiency owing to the shuttling of lithium polysulfides (LiPSs) and irreversible discharge product Li2S. Here, by means of first principles calculations, we studied defective black phosphorene (BP) as a host material to realize high-performance Li-S batteries, including Stone Wales [SW(55-77)], single, and double vacancy [SV(5-9) and DV(5-9-5)] defects. Our results demonstrate that while BP has moderate adsorption energies towards LiPSs, the presence of defects could enhance the adsorption strength between LiPSs and BP because of increased charge transfer. Particularly, defective BP could strike a good balance between adsorption energy and integrity of LiPSs, which is beneficial to prevent the shuttling of LiPSs. Moreover, during the lithiation process, defective BP not only has narrow bandgaps but also decreases the dissociation energy of Li2S, facilitating the catalytic oxidation of Li2S back to sulfur. Therefore, it is highly desirable to fabricate defective BP to improve the reversible capacity and cycle stability of Li-S batteries. [ABSTRACT FROM AUTHOR]

Ln (Ln = La and Ce) atom reactions with ammonia are carried out in a pulsed laser vaporization supersonic molecular beam source. Lanthanide-containing species are observed with time-of-flight mass spectrometry, and LnNH molecules are characterized by mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical calculations. The theoretical calculations include density functional theory for both Ln species and a scalar relativity correction, electron correlation, and spin-orbit coupling for the Ce species. The MATI spectrum of LaNH exhibits a single vibronic band system with a strong origin band and two weak vibronic progressions, whereas the spectrum of CeNH displays two band systems separated by 75 cm−1 with each being like the LaNH spectrum. By comparing with the theoretical calculations, both LaNH and CeNH are identified as linear molecules with C∞v symmetry, and the two vibronic progressions are attributed to the excitations of Ln–N stretching and Ln–N–H bending modes in the ions. The additional band system observed for CeNH is due to the spin-orbit splitting from the interactions of triplet and singlet states. The ground valence electron configurations of LaNH and CeNH are La 6s1 and Ce 4f16s1, and the ionization of each species removes the Ln 6s1 electron. The remaining two electrons that are associated with the isolated Ln atoms or ions are in a doubly degenerate molecular orbital that is a bonding combination between Ln 5dπ and N pπ orbitals. [ABSTRACT FROM AUTHOR]

La atom reactions with 1-pentene and 2-pentene are carried out in a laser-vaporization molecular beam source. The two reactions yield the same metal-hydrocarbon products from the dehydrogenation and carbon–carbon bond cleavage of the pentene molecules. The dehydrogenated species La(C5H8) is the major product, whereas the carbon–carbon bond cleaved species La(C2H2) and La(C3H4) are the minor ones. La(C10H18) is also observed and is presumably formed by La(C5H8) addition to a second pentene molecule. La(C5H8) and La(C2H2) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species from the two reactions exhibit the same transitions. Adiabatic ionization energies and metal-ligand stretching frequencies are determined for the two species, and additional methyl bending and torsional frequencies are measured for the larger one. Five possible isomers are considered for La(C5H8), and a C1 metallacyclopentene (Iso A) is identified as the most possible isomer. La(C2H2) is confirmed to be a C2v metallacyclopropene. The ground electronic state of each species is a doublet with a La 6s1-based electron configuration, and ionization yields a singlet state. The formation of the lanthanacyclopentene includes La addition to the C=C double bond, La insertion into two C(sp3)—H bonds, and concerted dehydrogenation. For the 2-pentene reaction, the formation of the five-membered ring may also involve 2-pentene to 1-pentene isomerization. In addition to the metal addition and insertion, the formation of the three-membered metallacycle from 1-pentene includes C(sp3)—C(sp3) bond breakage and hydrogen migration from La to C(sp3), whereas its formation from 2-pentene may involve the ligand isomerization. [ABSTRACT FROM AUTHOR]

La atom reaction with isoprene is carried out in a laser-vaporization molecular beam source. The reaction yields an adduct as the major product and C—C cleaved and dehydrogenated species as the minor ones. La(C5H8), La(C2H2), and La(C3H4) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of all three species exhibit a strong origin band and several weak vibronic bands corresponding to La-ligand stretch and ligand-based bend excitations. La(C5H8) is a five-membered metallacycle, whereas La(C2H2) and La(C3H4) are three-membered rings. All three metallacycles prefer a doublet ground state with a La 6s1-based valence electron configuration and a singlet ion. The five-membered metallacycle is formed through La addition and isoprene isomerization, whereas the two three-membered rings are produced by La addition and insertion, hydrogen migration, and carbon-carbon bond cleavage. [ABSTRACT FROM AUTHOR]

The analysis and detection of nucleic acid and specific antigens and antibodies are the most basic technologies for virus monitoring. However, the potential window for applying these technologies exists within a late specific period in the early monitoring and control of unknown viruses, especially human and animal pathogenic viruses transmitted via aerosols, e.g., SARS-CoV-2 and its variants. This is because early, real-time, and convenient monitoring of unknown viruses in the air or exhaled gas cannot be directly achieved through existing technologies. Herein, we report a weak light spectral imaging technology based on Tesla discharge (termed T-DAI) that can quickly monitor for viruses in real time in simulated aerosols with 71% sensitivity and 76% specificity for aerosol virus concentrations exceeding approximately 2800 vp/μl. This technology realizes the rapid detection of low concentrations of viruses in aerosols and could provide an important means for predicting, screening, and monitoring unknown or pandemic pathogenic viruses in the air or exhaled breath of humans and animals. [ABSTRACT FROM AUTHOR]

Cr2O3 has been recognized as a key oxide component in bifunctional catalysts to produce bridging intermediate, e.g., methanol, from syngas. By combining density functional theory calculations and microkinetic modeling, we computationally studied the surface structures and catalytic activities of bare Cr2O3 (001) and (012) surfaces, and two reduced (012) surfaces covered with dissociative hydrogens or oxygen vacancies. The reduction of (001) surface is much more difficult than that of (012) surface. The stepwise or the concerted reaction pathways were explored for the syngas to methanol conversion, and the hydrogenation of CO or CHO is identified as rate-determining step. Microkinetic modeling reveals that (001) surface is inactive for the reaction, and the rates of both reduced (012) surfaces (25−28 s−1) are about five times higher than bare (012) surface (4.3 s−1) at 673 K. These theoretical results highlight the importance of surface reducibility on the reaction and may provide some implications on the design of individual component in bifunctional catalysis. [ABSTRACT FROM AUTHOR]

The one-step conversion of ethanol to 1,3-butadiene has achieved a breakthrough with the development of beta zeolite supported dual metal catalysts. However, the reaction mechanism from ethanol to butadiene is complex and has not yet been fully elucidated, and no catalyst screening effort has been done based on central metal atoms. In this work, density functional theory (DFT) calculations were employed to study the mechanism of one-step conversion of ethanol to butadiene over Zn-Y/BEA catalyst. The results show that ethanol dehydrogenation prefers to proceed on Zn site with a reaction energy of 0.77 eV in the rate-determining step, and the aldol condensation to produce butadiene prefers to proceed on Y site with a reaction energy of 0.69 eV in the rate-determining step. Based on the mechanism revealed, six elements were selected to replace Y for screening superior combination of Zn-M/BEA (M=Sn, Nb, Ta, Hf, Zr, Ti; BEA: beta polymorph A) for this reaction. As a result, Zn-Y/BEA (0.69 eV) is proven to be the most preferring catalyst compared with the other six ones, and Zn-Zr/BEA (0.85 eV), Zn-Ti/BEA (0.87 eV), and Zn-Sn/BEA (0.93 eV) can be potential candidates for the conversion of ethanol to butadiene. This work not only provides mechanistic insights into one-step catalytic conversion of ethanol to butadiene over Zn-Y/BEA catalyst but also offers more promising catalyst candidates for this reaction. [ABSTRACT FROM AUTHOR]

To investigate the decomposition law of SF6 under negative direct current partial discharge (PD) at different energies, a SF6 PD hybrid numerical model based on fluid dynamics and plasma chemical reaction models, in which 14 particle species and 24 chemical reactions are considered, is proposed. The effectiveness of the proposed model is validated with the current pulse waveform and the V–I discharge curve obtained by experiment. The influence of discharge energy on SF6 PD characteristic quantities and SF6 decomposition products is investigated with simulation and experiment. The results show that most of the discharge area of SF6 is neutral, and the cation clouds only exist in the ionosphere (4.79–5 mm). With the increase in applied voltage, the electric field intensity of the needle plate gap does not increase completely and even decreases in some areas. Moreover, different from the traditional opinion, the generation of SO2F2 under PD is mainly generated by the hydrolysis reaction of SOF4, which is formed by [SF5], [SF4], and [OH], [O]. The reaction path of [SF2] with O2 is not important. Thus, c(SO2F2)/c(SOF2 + SO2) can be used as the energy characteristic component ratio because of its ability to represent the low-fluorine sulfide ratio n([SF5])/n([SF4]). [ABSTRACT FROM AUTHOR]

The S1 state decay dynamics of 2-hydroxypyridine following UV excitation at a wavelength range of 276.9−250.0 nm is investigated using femtosecond time-resolved photoelectron imaging technique. Based on pump wavelength dependence of the decay dynamics, a refined decay picture is proposed. At pump wavelength of 276.9 nm, the S1 state is depopulated through intersystem crossing to lower triplet state(s). At 264.0 nm, both intersystem crossing to lower triplet state(s) and internal conversion to the ground state are in operation. At 250.0 nm, internal conversion to the ground state becomes dominated. [ABSTRACT FROM AUTHOR]

The generic problem of low-frequency acoustic radiation through quiescent air from a circular pipe that is inclined with respect to its exit flange is studied in this work. The exit flange is taken to extend as an infinite plane away from the pipe opening. The analysis implements a hybrid method that combines modal expansions with the boundary element method. The reflection coefficient and pipe end correction for Helmholtz numbers (based on the pipe radius) less than 2.5 are calculated for various inclination angles up to 75°. Calculations are validated using simulations from the finite-element solver of the commercial software package COMSOL. The reflection coefficient and end correction predictions agree closely with the validation simulations yet differ notably from the results available in the literature. The solution obtained from the hybrid method is subsequently used to analyse the acoustic field at the pipe exit and in the downstream space. The key aspects of the governing physics pertaining to practical engineering applications at low frequencies are captured in a low-order approximation, which significantly reduces the degrees of freedom of the problem and provides generally good estimates of the reflection coefficient and end correction, as well as the downstream acoustic field. [ABSTRACT FROM AUTHOR]

The plasma arc caused by lightning overvoltage can significantly degrade the power grid reliability. Thus, it is essential to design an efficient arc extinguishing system. The modeling and analysis of the plasma arc in an arc extinguishing system can provide an essential theoretical basis for improving and optimizing its structure. However, the precision of the governing equation and boundary value of the plasma arc model chosen in previous studies can be entirely different from the corresponding practical values. This study develops an arc extinguishing system named "convective shock wave complex system." In order to further optimize its structure and achieve a better arc extinguishing effect, an appropriate model is established to analyze the plasma's operation characteristics inside the arc extinguishing device while stroking by lightning. Based on the magnetohydrodynamics theory, the COMSOL software is utilized to analyze the temperature of the plasma arc, the flow rate of gas in the cavity, and the conductivity and current density of some monitoring points to comprehensively analyze the plasma's physical characteristics in the system. Finally, a virtual lightning experiment is utilized to evaluate the simulation results. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials are attracting increasing research interest owing to their distinct tunable physical properties. Moreover, the ubiquitous defects in 2D materials offer an opportunity to tailor their electronic properties. Recently, atomic-level structural modification methods for 2D materials have been developed, further triggering the need for the precise control of defects. Following the ground-breaking advancements in the atomic-scale characterization of defects in 2D materials, valuable information on defect-driven electronic properties has been published. It is therefore important to present a review work on the recent research developments on atomic-level defect control and characterization of 2D materials. This Perspective highlights the type and role of atomic defects in 2D materials, as well as some current technologies for engineering such defects. In addition, we emphasize on atomic-level characterization methods with a focus on aberration-corrected transmission electron microscopy and deep learning as a powerful method for characterizing defects in 2D materials. Based on the two characterization techniques, we present the experimental results of laser-induced structurally modified MoTe2 and transition metal decorated h-BN. We believe that this work will provide fundamental knowledge for engineering and characterizing defects in 2D materials for the design of application-specific electronic devices. [ABSTRACT FROM AUTHOR]

Multi-bifurcation behaviors of staged swirl flames fueled with methane at atmospheric pressure are experimentally investigated by varying the global equivalence ratio ( ϕ glo ). Based on the characteristics of measured pressure oscillations and the associated results of phase space reconstruction, recurrence plots, and synchrosqueezing-transform-based time-frequency analysis, the multi-bifurcation behaviors of this thermoacoustic system with four different stability regimes have been identified. With incremental increase in ϕ glo from 0.55 to 0.79, these four stability regimes follow the sequence of a quiet mode (Regime I), the first limit cycle with moderate oscillations (Regime II), an intermediate state with intermittent bursts of multi-modes (Regime III), and the second limit cycle with much stronger oscillations (Regime IV). The flame dynamics in Regimes II and IV undergoing limit cycle oscillations are compared. The flame structure in Regime II displays an attached twin-flame structure, the same as that observed in Regime I. However, a large-scale periodic convective motion is found in Regime IV, which is identified to be the main thermoacoustic driving factor in the local Rayleigh index maps. Further experiments are carried out by continuously increasing ϕ glo to examine the synchrosqueezing-transform spectra of transient processes during the two bifurcations. The present investigation is instrumental in obtaining a fundamental understanding of nonlinearity and multi-bifurcation of thermoacoustic instabilities in centrally staged swirl combustors, which is vital in guiding the early stage design and developing detection/control strategies in practical low-emission combustion systems. [ABSTRACT FROM AUTHOR]

N -ethylpyrrole is one of ethyl-substituted derivatives of pyrrole and its excited-state decay dynamics has never been explored. In this work, we investigate ultrafast decay dynamics of N - ethylpyrrole excited to the S1 electronic state using a femtosecond time-resolved photoelectron imaging method. Two pump wavelengths of 241.9 and 237.7 nm are employed. At 241.9 nm, three time constants, 5.0±0.7 ps, 66.4±15.6 ps and 1.3±0.1 ns, are derived. For 237.7 nm, two time constants of 2.1±0.1 ps and 13.1±1.2 ps are derived. We assign all these time constants to be associated with different vibrational states in the S1 state. The possible decay mechanisms of different S1 vibrational states are briefly discussed. [ABSTRACT FROM AUTHOR]

The x-ray emissivity of gadolinium (Gd) and gold (Au) has been studied using the FLYCHK code. The results show that the Gd M-band is lower than 2 keV and that Gd has a higher x-ray emissivity at low temperature. Thus, we proposed a Gd + Au + Gd sandwich design to improve the x-ray conversion efficiency (CE). Under a laser intensity of 1 × 1015 W/cm2, a 11%–17% enhancement of the CE and an optimized x-ray spectrum were achieved in one-dimensional simulation. The enhancement of the CE is mainly due to an enhancement of the soft x-ray flux (0 keV–2 keV). In addition, the high energy x-ray flux (2 keV–5 keV) is lower than that of Au. Particularly at an early stage, the laser ablates the Gd layer, and the temperature of the Au layer is insufficient for producing an M-band emission. Thus, the high energy x-ray flux is rather low. A sandwich design not only takes advantage of the higher x-ray emissivity of Gd under specific conditions in an efficient manner but also simplifies the target fabrication, which is important. In addition, Gd can also be used to optimize the future design of depleted uranium Hohlraum. [ABSTRACT FROM AUTHOR]

We present particle-in-cell (PIC) simulations of laser plasma instabilities (LPIs) with a laser pulse duration of a few picoseconds. The simulation parameters are appropriate to the planar-target LPI experimental conditions on SG-II. In this regime, the plasmas are characterized by a long electron density scale length and a large electron density range. It is found that when the incident laser intensity is well above its backward stimulated Raman scattering (backward SRS, BSRS) threshold, the backscattered light via the primary BSRS is intense enough to excite secondary SRS (Re-SRS) in the region below one-ninth of the critical density of the incident laser. The daughter light wave via the secondary BSRS (Re-BSRS) is amplified as it propagates toward the higher-density region in the bath of broadband light generated through the primary BSRS process. A higher intensity of the incident laser not only increases the amplitude of the BSRS light but also increases the convective amplification lengths of the Re-BSRS modes by broadening the spectrum of the BSRS light. Convective amplification of Re-BSRS causes pump depletion of the primary BSRS light and may lead to an underestimate of the primary BSRS level in SP-LPI experiments. A significant fraction of the generation of energetic electrons is strongly correlated with the Re-BSRS modes and should be considered as a significant energy loss. [ABSTRACT FROM AUTHOR]

A 100 kJ-level laser facility has been designed to study inertial confinement fusion physics in China. This facility incorporates various diagnostic techniques, including optical, x-ray imaging, x-ray spectrum, and fusion product diagnostics, as well as general diagnostics assistance systems and central control and data acquisition systems. This paper describes recent developments in diagnostics at the facility. [ABSTRACT FROM AUTHOR]

Infrared photodissociation spectroscopy of mass-selected [MO(CO2)n]+ (M=Sc, Y, La) complexes indicates that the conversion from the solvated structure into carbonate one can be achieved by the ScO+ cation at n=5 and by the YO+ cation at n=4, while only the solvated structures are observed for the LaO+ cation. These findings suggest that both the ScO+ and YO+ cations are able to fix CO2 into carbonate. Quantum chemical calculations are performed on [MO(CO2)n]+ to identify the structures of the low-lying isomers and to assign the observed spectral features. Theoretical analyses show that the [YO(CO2)n]+ complex has the smallest barrier for the conversion from the solvated structure into carbonate one, while [LaO(CO2)n]+ exhibits the largest conversion barrier among the three metal oxide cations. The present system affords a model in clarifying the effect of different metals in catalytic CO2 transformation at the molecular level. [ABSTRACT FROM AUTHOR]

This paper describes an experimental technique for studying neutral metal complexes using infrared + vacuum ultraviolet (IR+VUV) two-color ionization spectroscopy based on a tunable VUV free-electron laser (VUV-FEL). The preliminary IR spectroscopy results of mass-selected nickel tetracarbonyl are reported in this work. The results demonstrate that the tunable VUV-FEL light allows the selective ionization of a given neutral cluster free of confinement along with the recording of well-resolved IR spectra. As the ionization energies of many neutral clusters are accessible by a broadly tunable VUV-FEL (50–150 nm) and near-threshold ionization can be readily achieved, the proposed experimental method offers unique possibilities for the size-specific study of a wide variety of confinement-free neutral clusters. [ABSTRACT FROM AUTHOR]

The structures, energetics, and infrared (IR) spectra of the cationic monomethylamine-water clusters, [(CH3NH2)(H2O)n]+ (n=1–5), have been studied using quantum chemical calculations at the MP2/6-311+G(2d,p) level. The results reveal that the formation of proton-transferred CH2NH3+ ion core structure is preferred via the intramolecular proton transfer from the methyl group to the nitrogen atom and the water molecules act as the acceptor for the O⋯HN hydrogen bonds with the positively charged NH3+ moiety of CH2NH3+, whose motif is retained in the larger clusters. The CH3NH2+ ion core structure is predicted to be less energetically favorable. Vibrational frequencies of CH stretches, hydrogen-bonded and free NH stretches, and hydrogen-bonded OH stretches in the calculated IR spectra of the CH2NH3+ and CH3NH2+ type structures are different from each other, which would afford the sensitive probes for fundamental understanding of hydrogen bonding networks generated from the radiation-induced chemical processes in the [(CH3NH2)(H2O)n]+ complexes. [ABSTRACT FROM AUTHOR]

In order to study the laser plasma instabilities (LPIs) in the context of some novel six-side laser-driven indirect designs like the six-cylinder-port hohlraum and the three-axis cylindrical hohlraum, where the laser beams inject in hohlraum with a large angle. LPI experiments in cylindrical hohlraum with only outer beams were designed and performed based on the current laser arrangement condition of SGIII laser facility for the first time. Stimulated Brillouin backscatter (SBS) was found to be the dominant instability with high instantaneous reflectivity in experiments. A typical feature was obtained in the time-resolved spectra of SBS, which maintained similar for different laser intensities of the interaction beam. The experimental data are analyzed by the hydrodynamic simulations combined with HLIP code, which is based on the ray-tracing model. By analysis of experimental data, it is argued that the mixture of gas and Au in the region of their interface is important to SBS, which indicates the need for the mixture model between the filled gas and the high Z plasma from hohlraum wall in the hydrodynamic simulations. Nonlinear saturation of SBS as well as the smoothed beam are also discussed here. Our effective considerations of the ions pervasion effect and the smoothed beam provide utilitarian ways for improvement of the current ray-tracing method. [ABSTRACT FROM AUTHOR]

The technique of x-ray fluorescence imaging (XRFI) has been applied to the high-energy-density (HED) jet experiments on the SG-III prototype laser facility. The jet was produced by the interaction of the laser driven shock with the perturbed Ti disk. The fluorescence emission of the Ti ejecta was pumped by the V He-α emission and recorded using a Ross Pair Imager with an optimized configuration. We achieved a spatial resolution of 35 μm and a temporal resolution of 1 ns. We also developed a method to infer the density distribution of the jet from the fluorescence images and discussed the conditions under which this method was accurate. These experiments provided insight into the characteristics of a HED jet and implied that XRFI is a promising way for studying HED hydrodynamics. [ABSTRACT FROM AUTHOR]

The mass-selected infrared photodissociation (IRPD) spectroscopy was utilized to investigate the interactions of cationic cobalt with carbon dioxide molecules. Quantum chemical calculations were performed on the [Co(CO2)n]+ clusters to identify the structures of the low-lying isomers and to assign the observed spectral features. All the [Co(CO2)n]+ (n=2−6) clusters studied here show resonances near the CO2 asymmetric stretch of free CO2 molecule. Experimental and calculated results indicate that the CO2 molecules are weakly bound to the Co+ cations in an end-on configuration via a charge-quadrupole electrostatic interaction. The present IRPD spectra of [Co(CO2)n]+ clusters have been compared to those of Ar-tagged species ([Co(CO2)n]+-Ar), which would provide insights into the tagging effect of rare gas on the weakly-bounded clusters. [ABSTRACT FROM AUTHOR]

M-band flux asymmetry (MFA) may be another critical factor which can lead to low-mode distortion of implosion. We describe an experimental technique employing the x-ray fluorescence signature of material to investigate the MFA onto the capsule. Si was chosen to be the tracer layer since the inducing threshold for the K-shell fluorescence is much higher than soft x-ray but a little lower than M-band x-ray. The fluorescence images were recorded from a surrogate Si-coated ball, and thus, the P2 MFA was deduced from the fluorescence images. [ABSTRACT FROM AUTHOR]

The ultrafast dynamics of water molecules excited to the two F̃ states is studied by combining two-photon excitation and time-resolved photoelectron imaging techniques. The lifetimes of the F̃1A1 and F̃1B1 states of H2O (D2O) were derived to be 1.0±0.3 (1.9±0.4) and 10±3 (30±10) ps, respectively. We propose that the F̃1A1 state mainly decays through the D̃ state, due to the nonadiabatic coupling between them, while the F̃1B1 state decays through the F̃1A1 state via Coriolis interaction. [ABSTRACT FROM AUTHOR]

The integral cross sections and rate constants of pure rotational and ro-vibrational energy transfer processes for the Ar-HF system are thoroughly studied by using the time-independent close coupling method based on our newly constructed potential energy surface. Compared to previous theoretical results, pure rotational transitions in this work achieve better agreement with the experimental data. For ro-vibrational energy transfer, it is found that quasi-resonant transitions dominate the cross sections in all cases. Furthermore, the vibrational-resolved rate constant of transition v=1→v=0 increases very quickly with the temperature from 100 K to 1500 K and is also in good agreement with the available experimental results. [ABSTRACT FROM AUTHOR]

An ultraviolet Thomson-scattering system has been designed and implemented on the Shenguang-III laser facility, a 48-beam, 3ω (351 nm), 180 kJ-level laser driver for high energy density physics and inertial confinement fusion researches. The 4ω (263.3 nm) probe beam of the Thomson-scattering system is injected from the north pole (top) of the target chamber, with an assistant beam-pointing monitor to achieve high pointing accuracy. The Thomson-scattered light is collected by a double-Cassegrain optical transmission system, which provides an achromatic image over a wide wavelength range of 200–800 nm. A novel on-line alignment method is developed and applied to the diagnostic system, ensuring a volumetric positioning accuracy of ∼30 μm for the scattering volume. An online calibration is also conducted to provide the wavelength benchmark and the spectral resolution of the system. This Thomson-scattering system has been tested in a complicated experimental environment with gas-filled hohlraums, and a high-quality ion feature of the scattered light has been obtained. [ABSTRACT FROM AUTHOR]

Space-resolving flux detection is an important technique for the diagnostic of the radiation field within the hohlraum in inertial confinement fusion, especially for the radiation field diagnostic in the novel spherical hohlraum with octahedral six laser entrance holes (LEHs), where localized measurements are necessary for the discrimination of the radiation flux from different LEHs. A novel space-resolving flux detector (SRFD) is developed at the SG-III laser facility for the radiation flux measurement in the first campaign of the octahedral spherical hohlraum energetics experiment. The principle and configuration of the SRFD system is introduced. The radiation flux from the wall of a gas-filled octahedral spherical hohlraum is measured for the first time by placing the SRFD system at the equatorial position of the SG-III laser facility, aiming at the hohlraum wall through one of the six LEHs. The absolute radiation flux from the re-emission area on the hohlraum wall is measured, and good consistency is found between the experimental data and the calculated data from a three-dimensional view factor analysis. [ABSTRACT FROM AUTHOR]