1s Level Research Articles

Meson exchange in lepton-nucleon scattering and the proton radius puzzle

We study two-photon contribution to the elastic lepton-proton scattering, associated with sigma meson exchange, with special attention paid to the low-Q2 region. We show that the corresponding amplitude grows sharply but remains finite at Q2->0. The analytical formula for the amplitude at Q2=0 is obtained. We also estimate the shift of the muonic hydrogen energy levels, induced by sigma meson exchange. For the 2S level the shift is approximately 30 times smaller than needed to resolve the proton radius puzzle, but still exceeds the precision of the muonic hydrogen measurements.

Density diagnostics of ionized outflows in active galactic nuclei

Ionized outflows in Active Galactic Nuclei (AGN) are thought to influence their nuclear and local galactic environment. However, the distance of the outflows with respect to the central engine is poorly constrained, which limits our understanding of their kinetic power as a cosmic feedback channel. Therefore, the impact of AGN outflows on their host galaxies is uncertain. However, when the density of the outflows is known, their distance can be immediately obtained from their modelled ionization parameter. With the new self-consistent PhotoIONization (PION) model in the SPEX code, we are able to calculate detailed level populations, including the ground and metastable levels. This enables us to determine under what physical conditions the metastable levels are significantly populated. We then identify characteristic lines from these metastable levels in the 1 -- 2000 {\AA} wavelength range. In the large density range of $n_H \in (10^6, 10^{20} m^{-3}$, the metastable levels 2s 2p $(^3P_{0-2})$ in Be-like ions can be significantly populated. For B-like ions, merely the first excited level 2s$^2$ 2p $(^2P_{3/2})$ can be used as a density probe. For C-like ions, the first two excited levels 2s$^2$ 2p$^2$ ($^3P_1$ and $^3P_2$) are better density probes than the next two excited levels 2s$^2$ 2p$^2$ ($^1S_0$ and $^1D_2$). Different ions in the same isoelectronic sequence cover not only a wide range of ionization parameter, but also a wide range of density. On the other hand, within the same isonuclear sequence, less ionized ions probe lower density and smaller ionization parameter. Finally, we re-analyzed the high-resolution grating spectra of NGC 5548 observed with Chandra in January 2002, using a set of PION components to account for the ionized outflow. We derive lower (or upper) limits of plasma density in five out of six PION components, based on the presence (or absence) of the metastable absorption lines.

Experimental study of the electric field in a hollow cathode discharge in hydrogen: influence of sputtering

Doppler-free two photon optogalvanic spectroscopy was employed in extensive studies to measure the electric field strength in the cathode fall region of a hollow cathode discharge (HCD), operated in pure hydrogen, via the Stark splitting of the 2S level of atomic hydrogen. The high quality measurements, based on an improved cathode design and laser spectroscopic set-up, reveal clear differences in the recorded spectra obtained for different cathode material (stainless steel and tungsten) at otherwise identical discharge conditions. It is well known, that the sputtering rate of tungsten is about four orders of magnitude less compared to stainless steel; hence the hydrogen plasma in front of the stainless steel cathode is much more contaminated by iron compared to tungsten. This study is focussed on analyzing the distortion of the spectra, i.e. the corresponding local electric field strength, depending on cathode material and laser power. We refer the more pronounced distortion of the spectra in case of a stainless steel cathode to the related large contamination of the hydrogen plasma due to atomic iron which is also expanding into the central discharge. Spectra recorded for different laser power, i.e. different spectral irradiance, allow verifying spectroscopic conditions, where the distortion of the spectra becomes quite negligible even for stainless steel cathode.

Constraining the K¯N interaction from the 1S level shift of kaonic deuterium

Motivated by the precise measurement of the 1S level shift of kaonic hydrogen, we perform accurate three-body calculations for the spectrum of kaonic deuterium using a realistic antikaon-nucleon (K¯N) interaction. In order to describe both short- and long-range behaviors of the kaonic atomic states, we solve the three-body Schrodinger equation with a superposition of a large number of correlated Gaussian basis functions covering distances up to several hundreds of fm. Transition energies between 1S,2P, and 2S states are determined with high precision. The complex energy shift of the 1S level of kaonic deuterium is found to be ΔE−iΓ/2=(670−i508) eV. The sensitivity of this level shift with respect to the isospin I=1 component of the K¯N interaction is examined. It is pointed out that an experimental determination of the kaonic deuterium level shift within an uncertainty of 25% will provide a constraint for the I=1 component of the K¯N interaction significantly stronger than that from kaonic hydrogen.

X-ray reflectivity and photoelectron spectroscopy of superlattices with silicon nanocrystals

The structural properties and features of the chemical composition of SiO x N y /SiO2, SiO x N y /Si3N4, and SiN x /Si3N4 multilayer thin films with ultrathin (1–1.5 nm) barrier SiO2 or Si3N4 layers are studied. The films have been prepared by plasma chemical vapor deposition and have been annealed at a temperature of 1150°С for the formation of silicon nanocrystals in the SiO x N y or SiN x silicon-rich layers with a nominal thickness of 5 nm. The period of superlattices in the studied samples has been estimated by X-ray reflectivity. The phase composition of superlattices has been studied by X-ray electron spectroscopy using the decomposition of photoelectron spectra of the Si 2p, N 1s, and O 1s levels into components corresponding to different charge states of atoms.

Measured cathode fall characteristics depending on the diameter of a hydrogen hollow cathode discharge

In this work, Doppler-free two photon optogalvanic spectroscopy is used to measure the electric field strength in the cathode fall region of a hollow cathode discharge, operated in pure hydrogen, via the Stark splitting of the 2S level of atomic hydrogen. The cathode fall characteristics are analysed for various pressures and in a wide range of discharge currents. Tungsten is used as the cathode material, because it allows for reliable measurements in a fairly wide range of discharge conditions and because of its minimal sputtering. Two cathode diameters (10 mm and 15 mm) are used to study the dependence of the cathode fall on discharge geometry. The measurements reveal that the cathode fall characteristics are quite independent on the cathode diameter for equal cathode current density; hence the measurements can be used to test one dimensional modelling of the cathode fall region for low pressure hydrogen discharges using e.g. plane parallel electrodes.

Magnetic properties, x-ray absorption spectroscopy and electronic structure of GdCrTiO5

We study the electronic structure of GdCrTiO5 polycrystals by means of magnetic susceptibility and heat capacity measurements, as well as x-ray absorption spectroscopies on the Cr 2p, Ti 2p and O 1s levels. The experimental results were interpreted with Charge Transfer Multiplet and Density Functional Theory calculations. Magnetic susceptibility and specific heat measurements indicate a long-range antiferromagnetic ordering at 0.9 K probably related to the Gd sublattice. The results indicate that spin-orbit interaction, rather than hybridization, may be crucial for the stabilization of magnetic ordering in the RCrTiO5 (R = rare earth) family.

THE EFFECT OF TWO MANDIBULAR CLASS I REMOVABLE PARTIAL DENTURE DESIGNS ON THE PERIODONTAL HEALTH OF THE ABUTMENT TEETH: A RANDOMIZED SPLIT-MOUTH CLINICAL TRIAL

The aim of this study was to assess the effect of RPI direct retainer designs in mandibular Kennedy’s class I removable partial denture cases, on the periodontal conditions of their abutment teeth.Materials and methods: A total of 10 systemically healthy Patients were selected with mandibular Kennedy class I with symmetrical healthy periodontium at first premolar abutments split mouth mandibular class I removable partial denture designs RPI, I-bar (Rest, proximal plate and I bar) in one side (side A) and a modified RPI clasp assembly (Rest, proximal plate connected by lingual bracing arm to the rest and I Bar) in other side (side B) were constructed. Clinical evaluation(gingival index, pocket depth and clinical attachment loss) and recording of GCF levels of Interlukin1s IL1 –β using ELISA were carried out for all patients at base line (time of denture insertion), 3 months and 6 months after denture insertion at mandibular free end saddle abutments.Results: A statistically significant increase in the mean IL-1s levels after 3 months with further significant increase after 6 months was recorded in both sides (P ≤ 0.05) further, side B showed a statistically increased IL-β levels compared to side A. Regarding clinical parameters, side B showed a statistical significant increase at 6 months compared to side A regarding PD with no significant difference between the 2 sides at 3 months ,as for CAL and GI, although side B showed an increased readings in 6 months and 3 months compared to side A, a non significant difference was recorded between the 2 sides, as well, a non significant change in GI and CAL was recorded in both sides over the study period .Conclusion: within the limitation of our study, the modified RPI clasp induced increasing of proinflammatory cytokines IL- 1s levels in GCF compared conventional RPI clasp assembly. Both Clasp designs have an effect on periodontal health of free end saddle’s partial denture abutments.

VIP-2 at LNGS: An experiment on the validity of the Pauli Exclusion Principle for electrons

We are experimentally investigating possible violations of standard quantum mechanics predictions in the Gran Sasso underground laboratory in Italy. We test with high precision the Pauli Exclusion Principle and the collapse of the wave function (collapse models). We present our method of searching for possible small violations of the Pauli Exclusion Principle (PEP) for electrons, through the search for “anomalous” X-ray transitions in copper atoms. These transitions are produced by “new” electrons (brought inside the copper bar by circulating current) which can have the possibility to undergo Pauli-forbidden transition to the 1s level already occupied by two electrons. We describe the VIP2 (VIolation of the Pauli Exclusion Principle) experimental data taking at the Gran Sasso underground laboratories. The goal of VIP2 is to test the PEP for electrons in agreement with the Messiah-Greenberg superselection rule with unprecedented accuracy, down to a limit in the probability that PEP is violated at the level of 10−31. We show preliminary experimental results and discuss implications of a possible violation.

The stabilities and electron structures of Al-Mg clusters with 18 and 20 valence electrons

The spherical jellium model predicts that metal clusters having 18 and 20 valence electrons correspond to the magic numbers and will show specific stabilities. We explore in detail the geometric structures, stabilities and electronic structures of Al-Mg clusters containing 18 and 20 valence electrons by using genetic algorithm combined with density functional theories. The stabilities of the clusters are governed by the electronic configurations and Mg/Al ratios. The clusters with lower Mg/Al ratios are more stable. The molecular orbitals accord with the shell structures predicted by the jellium model but the 2S level interweaves with the 1D levels and the 2S and 1D orbitals form a subgroup. The clusters having 20 valence electrons form closed 1S21P61D102S2 shells and show enhanced stability. The Al-Mg clusters with a valence electron count of 18 do not form closed shells because one 1D orbital is unoccupied. The ionization potential and electron affinity are closely related to the electronic configurations; their values are determined by the subgroups the HOMO or LUMO belong to.

Spectroscopic properties of Pr3+-doped 20Al(PO3)3-80LiF glasses as potential scintillators for neutron detection

We investigate the spectroscopic properties of praseodymium (Pr3+)-doped APLF glasses [20Al(PO3)3−80LiF+xPrF3, x=0.5 to3.0mol%] to realize their potential application as scintillators for neutron detection. From the ultraviolet (UV) to the near infrared (NIR) region, the Pr3+-doped glasses exhibit absorption and emission peaks which correspond to the different interconfigurational 4f5d and intraconfigurational 4f transitions of Pr3+ ions usually located within different environments of the glass matrix. The spectroscopy results also indicate that Pr3+ ions in APLF have a 4f5d excited state configuration which overlaps with the 1S0 level of the 4f ground state configuration. Under 217 nm excitation, the 267 nm emissions of the Pr3+-doped APLF glasses which correspond to the 4f5d → 3H6 transition have fast lifetimes ranging from 16.0 to 19.7ns. In contrast with emission intensities, the emission lifetimes are found to depend only on the doping concentration and not on the sample temperature. Our results suggest that Pr3+-doped APLF glasses can be used as neutron scintillators with robustness in a wide temperature range and with fast and intense emissions at low operating temperatures.

Thermally induced anchoring of a zinc-carboxyphenylporphyrin on rutile TiO2 (110)

Functionalization of surfaces has become of high interest for a wealth of applications such as sensors, hybrid photovoltaics, catalysis, and molecular electronics. Thereby molecule-surface interactions are of crucial importance for the understanding of interface properties. An especially relevant point is the anchoring of molecules to surfaces. In this work, we analyze this process for a zinc-porphyrin equipped with carboxylic acid anchoring groups on rutile TiO2 (110) using scanning probe microscopy. After evaporation, the porphyrins are not covalently bound to the surface. Upon annealing, the carboxylic acid anchors undergo deprotonation and bind to surface titanium atoms. The formation of covalent bonds is evident from the changed stability of the molecule on the surface as well as the adsorption configuration. Annealed porphyrins are rotated by 45° and adopt another adsorption site. The influence of binding on electronic coupling with the surface is investigated using photoelectron spectroscopy. The observed shifts of Zn 2p and N 1s levels to higher binding energies indicate charging of the porphyrin core, which is accompanied by a deformation of the macrocycle due to a strong interaction with the surface.

Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering.

The femtosecond excited‐state dynamics following resonant photoexcitation enable the selective deformation of N−H and N−C chemical bonds in 2‐thiopyridone in aqueous solution with optical or X‐ray pulses. In combination with multiconfigurational quantum‐chemical calculations, the orbital‐specific electronic structure and its ultrafast dynamics accessed with resonant inelastic X‐ray scattering at the N 1s level using synchrotron radiation and the soft X‐ray free‐electron laser LCLS provide direct evidence for this controlled photoinduced molecular deformation and its ultrashort timescale.

On the possibility of laser generation without inversion on the fine-structure levels of a helium atom

It is shown that laser generation is possible in principle upon coherent excitation according to the V-scheme of the (1s2p)3Pj levels with j = 1, 2 of a helium atom from the (1s2s)3S1 level of the same atom when the latter level is, in turn, populated by electron or proton impact.

Modeling nightglow in atomic oxygen red and green lines under moderate disturbed geomagnetic conditions at midlatitudes

We present results of a study of mid-latitude auroras. The study is based on optical measurements and theoretical modeling. The modeling shows that precipitation can indirectly generate airglow in red and green lines of atomic oxygen by increasing rates of ion formation and heating of thermal electrons. This causes an increase in the rate of dissociative recombination and thermal-electron-collision excitation of the 1D and 1S levels.

Optogalvanic spectroscopy applied to the study of hollow cathode discharges devices

Doppler free two-photon optogalvanic spectroscopy has been applied to measure the electric field strength in the cathode fall region of a hollow cathode discharge, via the Stark splitting of the 2S level of atomic hydrogen. Important improvements in the experimental arrangement and in our understanding of the discharge, have allowed us to measure accurately the dependence of the electric field with different parameters like the cathode material (stainless steel and tungsten), geometry (10 and 15 mm inner diameter) and the buffer gas. The study is done for different pressures and currents. The first results seem to reveal different behaviour in the electric field, depending on the material and geometry of the cathode and the discharge conditions.

Different Properties of the $$\varvec{\bar{K}NN}$$ K ¯ N N and $$\varvec{\bar{K}\bar{K}N}$$ K ¯ K ¯ N Systems

A series of exact or accurate three-body calculations of different properties of the \(\bar{K}NN\) and \(\bar{K}\bar{K}N\) systems is described. In particular, binding energies and widths of the quasi-bound states in the systems were calculated. Near-threshold elastic \(K^- d\) amplitudes were also found together with the 1s level shift and width of kaonic deuterium. Different dependences of the three-body results on two-body inputs are discussed.

Моделирование ночных свечений красной и зеленой линий атомарного кислорода для умеренно-возмущенных геомагнитных условий на средних широтах

We present results of a study of mid-latitude auroras. The study is based on optical measurements and theoretical modeling. The modeling shows that precipitation can indirectly generate airglow in red and green lines of atomic oxygen by increasing rates of ion formation and heating of thermal electrons. This causes an increase in the rate of dissociative recombination and thermal-electron-collision excitation of the 1D and 1S levels.

Electron impact excitation with the cascade population of the 4p 5 5s levels of the krypton atom

Data are presented on the direct and effective, i.e., including the cascade population, electronic excitation cross sections of the 4p55s levels of the krypton atom from its ground state by the electron impact. The data are made up of the results available in the literature on this process and the results of the measurements performed by the authors.

Complex structures of dense lithium: Electronic origin

Lithium—the lightest alkali metal exhibits unexpected structures and electronic behavior at high pressures. Like the heavier alkali metals, Li is bcc at ambient pressure and transforms first to fcc (at 7.5 GPa). The post-fcc high-pressure form Li-cI 16 (at 40-60 GPa) is similar to Na-cI 16 and related to more complex structures of heavy alkalis Rb-oC52 and Cs- oC84. The other high pressure phases for Li (oC88, oC40, oC24) observed at pressures up to 130 GPa are found only in Li. The different route of Li high-pressure structures correlates with its special electronic configuration containing the only 3 electrons (at 1s and 2s levels). Crystal structures for Li are analyzed within the model of Fermi sphere-Brillouin zone interactions. Stability of post-fcc structures for Li are supported by the Hume-Rothery arguments when new diffraction plains appear close to the Fermi level producing pseudogaps near the Fermi level and decreasing the crystal energy. The filling of Brillouin-Jones zones by electron states for a given structure defines the physical properties as optical reflectivity, electrical resistivity and superconductivity. To understand the complexity of structural and physical properties of Li above 60 GPa it is necessary to assume the valence electron band overlap with the core electrons and increase the valence electron count under compression.