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Second-order-derivative plus fourth-order-derivative gravity is the ultraviolet completion of second-order-derivative quantum Einstein gravity. While it achieves renormalizability through states of negative Dirac norm, the unitarity violation that this would entail can be postponed to Planck energies. As we show in this paper, the theory has a different problem, one that occurs at all energy scales, namely that the Dirac norm of the vacuum of the theory is not finite. To establish this, we present a procedure for determining the norm of the vacuum in any quantum field theory. With the Dirac norm of the vacuum of the second-order-derivative plus fourth-order-derivative theory not being finite, the Feynman rules that are used to establish renormalizability are not valid, as is the assumption that the theory can be used as an effective theory at energies well below the Planck scale. This lack of finiteness is also manifested in the fact that the Lorentzian path integral for the theory is divergent. Because the vacuum Dirac norm is not finite, the Hamiltonian of the theory is not Hermitian. However, it turns out to be P T symmetric. When one continues the theory into the complex plane and uses the P T symmetry inner product, viz. the overlap of the left-eigenstate of the Hamiltonian with its right-eigenstate, one then finds that for the vacuum this norm is both finite and positive, the Feynman rules now are valid, the Lorentzian path integral now is well behaved, and the theory now can serve as a low energy effective theory, one that we show to have a real classical gravity limit. Consequently, the theory can now be offered as a fully consistent, unitary and renormalizable theory of quantum gravity. [ABSTRACT FROM AUTHOR]

This contribution is a survey of the available experimental radiation data measured in the VUV range related to hypersonic atmospheric entry. The objective is to identify the datasets already gathered during aerothermodynamics studies for preparing Mars, Venus, and sample return missions. The final goal is to identify the most valuable datasets for comparisons with future data measured in the European shock-tube ESTHER. Due to the limited number of studies covering VUV radiation in relation to space exploration missions, the review has been extended to domains such as nuclear fusion, exobiology, chemical and process engineering. [ABSTRACT FROM AUTHOR]

To more efficiently develop the single-atom catalysis, it is essential to deeply characterize the single-atom catalysis structure and study their catalytic mechanisms at the molecular and atomic scale. Herein, this paper reviews the advanced techniques for charactering the structure of single-atom combustion catalysis, including synchrotron-radiation based X-ray absorption spectroscopy (XAS) and spherical aberration-collected transmission electron microscopy. Meanwhile, synchrotron-tradiation based operando and in-situ techniques are introduced, including XAS, Fourier transform infrared (EQIR) and synchrotron vacuum ultraviolet radiation photoionization mass spectrometry (SVUV-PIMS), which could play vital roles in unravelling the reaction mechanisms. These advanced structural characterizations to investigate the existence of single-atom catalysis and their catalytic mechanisms would significantly provide a new vision for the design and synthesis of single-atom combustion catalysis. Furthermore, current challenges and future research directions of these characterization techniques in single-atom combustion catalysis are presented. 38 References are included. [ABSTRACT FROM AUTHOR]

In synchrotron radiation and electron storage rings, photon-stimulated gas desorption is a major contributor to gas load, leading to vacuum degradation and compromising the stability and quality of the beamline. Therefore, it is imperative to investigate the underlying mechanisms of photon-stimulated gas desorption to enhance the reliability of the experiments. In this paper, a theoretical model for analyzing the process of photon-stimulated desorption is presented, and the equations are solved numerically by considering the evacuation, bulk diffusion, thermal outgassing, adsorption, and desorption of surface gas molecules. The modified model can predict the yield of H 2 gas desorption induced by photon stimulation when synchrotron radiation is directed vertically onto various sample surfaces, utilizing the coupled multi-physics solution. The calculated results are consistent with the experimental measurements obtained from the Shanghai Synchrotron Radiation Facility. The results show that the photodesorption yield is related to the amount of surface-adsorbed molecules, which explains the observed decrease in the photodesorption yield with increasing accumulated photon dose. Furthermore, the study provides a theoretical approach to predicting the pressure evolution of photon-stimulated desorption. • A theoretical model for the analysis of photon-stimulated desorption (PSD) process is presented. • Reveals the mechanism underlying the decrease in the PSD yield with increasing accumulated photon dose. • Methods for predicting the evolution of pressure in the vacuum chamber before and after synchrotron radiation. • Methods for reducing the error between the tested PSD yield and the intrinsic PSD yield. [ABSTRACT FROM AUTHOR]

The low-lying electronic states of silicon dimer (Si 2 ) and its cation (Si 2 + ) have been studied by single-photon photoelectron spectroscopy combining a flow-tube reactor, vacuum-ultraviolet synchrotron radiation, and a double imaging photoelectron/photoion spectrometer. The energy range covered in this study (7.0−9.5 eV) allowed to observe several photoionising transitions involving the three lowest electronic states of Si 2 ( X 3 Σ g − , D 3 Π u , a 1 Δ g ) and five of the six lowest states of Si 2 + ( X + 4 Σ g − , a + 2 Π u , b + 2 Δ g , c + 2 Σ g − , and e + 2 Π u ). Using ab initio calculations and Franck-Condon simulations, several electronic transitions are identified which bring new elements in the description of the dense electronic landscapes of the silicon dimer and its cation. Interestingly, one of the most intense transitions is spin-forbidden ( X + 4 Σ g − ← a 1 Δ g ) and is most probably observed through autoionisation processes by spin interactions. [ABSTRACT FROM AUTHOR]

This study employed a vacuum ultraviolet synchrotron radiation source and reflectron time‐of‐flight mass spectrometry (TOF‐MS) to investigate the photoionization and dissociation of styrene. By analyzing the photoionization mass spectrum and efficiency curve alongside G3B3 theoretical calculations, we determined the ionization energy of the molecular ion, appearance energy of fragment ions, and relevant dissociation pathways. The major ion peaks observed in the photoionization mass spectra of styrene correspond to C8H8+, C8H7+ and C6H6+. The ionization energy of styrene is measured as 8.46 ± 0.03 eV, whereas the appearance energies of C8H7+ and C6H6+ are found to be 12.42 ± 0.03 and 12.22 ± 0.03 eV, respectively, in agreement with theoretical values. The main channel for the photodissociation of styrene molecular ions is the formation of benzene ions, whereas the dissociation channel that loses hydrogen atoms is the secondary channel. Based on the experimental results and empirical formulas, the required dissociation energies (Ed) of C8H7+, C8H6+ and C6H6+ are calculated to be (3.96 ± 0.06), (4.00 ± 0.06) and (3.76 ± 0.06) eV, respectively. Combined with related thermochemical parameters, the standard enthalpies of formations of C8H8+, C8H7+, C8H6+ and C6H6+ are determined to be 964.2, 1346.3, 1350.2 and 1327.0 kJ/mol, respectively. Based on the theoretical study, the kinetic factors controlling the styrene dissociation reaction process are determined by using the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. This provides a reference for further research on the atmospheric photooxidation reaction mechanism of styrene in atmospheric and interstellar environments. [ABSTRACT FROM AUTHOR]

Results are presented of research aimed at creating a compact source of soft X-ray and vacuum ultraviolet radiation through the collision of a powerful plasma flow with a gas jet. In experiments that were carried out, a pulsed electrodynamic accelerator generated a hydrogen plasma flow with an energy constant of ≈50 kJ and duration of 10–15 μs. The flow, with a density of ≈6 × 1015 cm–3, moved at a velocity of (2‒4) × 107 cm/s in a longitudinal magnetic field with an induction of up to 2 T and interacted with a flat supersonic gas jet. The maximum molecular density of the gas, nitrogen or neon, in the jet reached 1017 cm–3. The formation of a compact emitting plasma layer with a thickness of 3–5 cm, moving along the path of the hydrogen plasma flow at a speed of approximately 3 × 106 cm/s was demonstrated. In several experiments, a tungsten plate was used as an obstacle to confine the motion of the emitting plasma along the magnetic field, localizing the interaction region between the plasma flow and the gas jet within the diagnostic control zone. Soft X-ray obscurography and spectroscopy were used to obtain data regarding the radiation generation from the interaction zone of the hydrogen plasma flow and the gas jet. The results of measuring the radiation energy from the formed plasma are presented: ≈2 kJ in the case of a nitrogen jet and ≈ 3 kJ in the case of a neon jet. Numerical modeling of the line radiation from multi-charged ions and subsequent comparison of calculated and experimental data allowed estimating the electron temperature of the nitrogen and neon plasmas formed during the interaction of the hydrogen plasma flow with the gas jet at a level of ≥40 eV. [ABSTRACT FROM AUTHOR]

Carbon 1s excitation of methane, CH4, has been studied in the gas phase using the ion trap integrated with the photon–ion instrument at PETRA III/DESY and soft X-rays from the beamline P04. The created photoions are stored within the ion trap so that in further steps the photoions can undergo reactions with neutral methane molecules. The ionic photoproducts as well as reaction products created thereby are mass-over-charge analyzed by an ion time-of-flight spectrometer. Besides the photoions, product ions with up to three carbon atoms are found. In contrast to experiments using vacuum ultraviolet radiation, especially highly reactive product ions with a small number of hydrogen atoms such as C 2 H 2 + and C 2 H 3 + are found, which are important precursors for larger hydrocarbons such as C6H6. Possible production routes of the product ions are analyzed on the basis of a model that considers the probabilities for photofragmentation and the first subsequent chemical reaction step. The model indicates that the high degree of fragmentation by photons with energies around 280 eV is favoring these products. The results of the measurements show that the products like C 2 H 2 + and C 2 H 3 + can be generated by a single collision of the ionization product with neutral methane. The results suggest that soft X-rays might be important for chemical reactions in planetary atmospheres, which has usually not been taken into account. However, due to the high degree of fragmentation and large cross sections involved, they can have a large influence even when the corresponding photon flux is rather small. [ABSTRACT FROM AUTHOR]

The materials of the article outline the features of the use of ultraviolet LED systems in industry, and propose a solution for their use in the grain processing and compound feed industry. Ultraviolet light (UV) is a well-researched and widely used means of decontamination and disinfection of surfaces, air, water, and food. Usually, far ultraviolet radiation (or ultraviolet C, UVC) with a wavelength of 254 nm is used, which corresponds to the peak absorption of wave energy by the DNA of a living cell. There is a mathematical mechanism for calculating the parameters of radiation in relation to its effect on microorganisms: a curve describing the microbial death depending on the increase in the radiation dose received by the bacteria and formulae for the relationship between the three main parameters (dose, radiation flux and exposure duration). Ultraviolet lamps (tubes) are commonly used, on the basis of which a large number of emitters have been developed for different needs. There are also emitters for grain and feed disinfection in use, but only outside of industrial production lines. Ultraviolet irradiation is not used directly on manufacturing lines so far. However, it can be used to reduce the microbial burden of a feed or food product prior to packaging the finished product. For this purpose, ultraviolet light-emitting diodes (LEDs) available on the world market today can be used. However, their use faces difficulties: ultraviolet LEDs emit wavelengths longer than lamps (at about 275 nm or more), which requires an increase in the duration of irradiation, which is undesirable for industrial processing of products directly on the line. However, the small size of the UVC LEDs will allow them to be installed in grain processing and feed mills inside equipment (magnetic separators, gravity feeders, etc.) with appropriate protection against damage by moving material. In addition, suspended emitters of any configuration can be placed above belt conveyors that move material at a certain speed. This approach will require certain measures to control the efficiency of irradiation (requires microbiological studies) and to protect personnel from the harmful effects of ultraviolet rays (means of personal and collective protection, measurement of radiation intensity). [ABSTRACT FROM AUTHOR]

Polyetheretherketone (PEEK) is the material of choice in several applications ranging from the automotive industry to medicine, but the surface properties are usually not adequate. A standard method for tailoring surface properties is the application of gaseous plasma. The surface finish depends enormously on the processing parameters. This article presents a review of strategies adapted for improved wettability and adhesion of PEEK. The kinetics of positively charged ions, neutral reactive plasma species, and vacuum ultraviolet radiation on the surface finish are analyzed, and synergies are stressed where appropriate. The reviewed articles are critically assessed regarding the plasma and surface kinetics, and the surface mechanisms are illustrated. The directions for obtaining optimal surface finish are provided together with the scientific explanation of the limitations of various approaches. Super-hydrophilic surface finish is achievable by treatment with a large dose of vacuum ultraviolet radiation in the presence of oxidizing gas. Bombardment with positively charged ions of kinetic energy between about 100 and 1000 eV also enable high wettability, but one should be aware of excessive heating when using the ions. [ABSTRACT FROM AUTHOR]

This work presents a computational study of the atmospheric pressure plasma of the COST jet source in He + 0.1% N2 buffer gas, incorporating the treatment of the VUV resonant radiation from He atoms at a wavelength of 58.4 nm. The plasma is driven by single- and multi-frequency waveforms at various peak-to-peak voltages between 400 V and 685 V. The simulations, which include the photoemission of electrons from the electrodes as well as the photoionization of the N2 molecules indicate that these processes, induced by the VUV radiation, have relatively little influence on the discharge characteristics due to other more efficient charged particle production mechanisms, e.g., Penning ionization. While the plasma characteristics are computed along one spatial dimension perpendicular to the electrodes, the tracing of the VUV photons is executed in the real 3D geometry of the plasma source to allow the computation of the VUV photon flux leaving the device through the orifice. Photon fluxes up to ≈ 5 Ă— 1 0 15 cmâˆ'2 sâˆ'1, corresponding to an energy flux of ≈18 mW cmâˆ'2 are found at multi-frequency operation. [ABSTRACT FROM AUTHOR]

Oxygen plasma is widely used for enhancing the wettability of numerous polymers, including polyethylene terephthalate (PET). The treatment with plasma containing oxygen will cause surface functionalization with polar functional groups, which will, in turn, improve the wettability. However, the exact mechanisms leading to the hydrophilic or even super-hydrophilic surface finish are still insufficiently explored. The wettability obtained by plasma treatment is not permanent, since the hydrophobic recovery is usually reported. The mechanisms of hydrophobic recovery are reviewed and explained. Methods for suppressing this effect are disclosed and explained. The recommended treatment which assures stable hydrophilicity of PET samples is the treatment with energetic ions and/or vacuum ultraviolet radiation (VUV). The influence of various plasma species on the formation of the highly hydrophilic surface finish and stability of adequate wettability of PET materials is discussed. [ABSTRACT FROM AUTHOR]

• First systematic experimental study of OME oxidation with different chain lengths. • Species pool is dominated by oxygenates and nearly independent of the chain length. • Highest oxygenated intermediate of OME 1-5 combustion is methyl formate. • Reactivity: shift of the intermediate's peak for longer OMEs to lower temperatures. • Significant fractions of ethanol detected using photoionization spectroscopy. This paper presents a systematic study of oxymethylene ethers (OMEs) oxidation in an atmospheric laminar flow reactor setup. Oxymethylene ethers with different number of oxymethylene ether groups (n = 0–5) have been investigated under lean and rich conditions (750–1250 K). The flow reactor is coupled to an electron ionization molecular-beam mass spectrometer (EI-MBMS) with high mass resolution to measure speciation data. Additional isomer-selective speciation analysis was performed using a novel atmospheric laminar flow reactor combined with double-imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy at the vacuum ultraviolet radiation (VUV) beamline of the Swiss Light Source. The results show a dominance of oxygenated intermediates during the combustion of all OMEs in the investigated temperature regime. The observed species pool is thereby nearly independent of the OME's chain length. In particular the presence of significant fractions of ethanol is remarkable and indicates unknown or underestimated reaction pathways to form C–C bonds from OME structures. Formation of combustion intermediates during oxidation of longer OMEs occurs at lower temperatures and correlates with the ignition delay time. No hydrocarbons with more than four carbon atoms are detected. The combination of high mass resolution provided by EI-MBMS detection and isomer-selective analysis by i2PEPICO enables a complete overview of all intermediates. This allows for in-depth discussion and analysis of systematic trends for several intermediate species. [ABSTRACT FROM AUTHOR]

High-harmonic generation is a cornerstone of nonlinear optics. It has been demonstrated in dielectrics, semiconductors, semi-metals, plasmas, and gases, but, until now, not in metals. Here we report high harmonics of 800-nm-wavelength light irradiating metallic titanium nitride film. Titanium nitride is a refractory metal known for its high melting temperature and large laser damage threshold. We show that it can withstand few-cycle light pulses with peak intensities as high as 13 TW/cm2, enabling high-harmonics generation up to photon energies of 11 eV. We measure the emitted vacuum ultraviolet radiation as a function of the crystal orientation with respect to the laser polarization and show that it is consistent with the anisotropic conduction band structure of titanium nitride. The generation of high harmonics from metals opens a link between solid and plasma harmonics. In addition, titanium nitride is a promising material for refractory plasmonic devices and could enable compact vacuum ultraviolet frequency combs. High harmonic generation is a nonlinear optical phenomena and HHG from solid offers challenges and advantages over dilute media like gases. Here the authors report HHG from metallic thin film of titanium nitride and discuss the role of intraband current to HHG. [ABSTRACT FROM AUTHOR]

Modification and functionalization of polymer surface properties is desired in numerous applications, and a standard technique is a treatment with non-equilibrium gaseous plasma. Fluorinated polymers exhibit specific properties and are regarded as difficult to functionalize with polar functional groups. Plasma methods for functionalization of polyvinylidene fluoride (PVDF) are reviewed and different mechanisms involved in the surface modification are presented and explained by the interaction of various reactive species and far ultraviolet radiation. Most authors used argon plasma but reported various results. The discrepancy between the reported results is explained by peculiarities of the experimental systems and illustrated by three mechanisms. More versatile reaction mechanisms were reported by authors who used oxygen plasma for surface modification of PVDF, while plasma sustained in other gases was rarely used. The results reported by various authors are analyzed, and correlations are drawn where feasible. The processing parameters reported by different authors were the gas pressure and purity, the discharge configuration and power, while the surface finish was predominantly determined by X-ray photoelectron spectroscopy (XPS) and static water contact angle (WCA). A reasonably good correlation was found between the surface wettability as probed by WCA and the oxygen concentration as probed by XPS, but there is hardly any correlation between the discharge parameters and the wettability. [ABSTRACT FROM AUTHOR]