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[en] A method is proposed for calculating the rate constants of inelastic processes occurring during collisions of alkali metal atoms and their positive ions with hydrogen atoms and negative ions, taking into account the sublevels of the fine structure of alkali metal levels. The results of the application of the proposed method are presented in this paper based on the example of the KH and RbH collisional systems.
[en] In a multiverse setting, we expect to be situated in a universe that is exceptionally good at producing life. Though the conditions for what life needs to arise and thrive are currently unknown, many will be tested in the coming decades. Here we investigate several different habitability criteria, and their influence on multiverse expectations: Does complex life need photosynthesis? Is there a minimum timescale necessary for development? Can life arise on tidally locked planets? Are convective stars habitable? Variously adopting different stances on each of these criteria can alter whether our observed values of the fine structure constant, the electron to proton mass ratio, and the strength of gravity are typical to high significance. This serves as a way of generating predictions for the requirements of life that can be tested with future observations, any of which could falsify the multiverse scenario.
[en] Crystallization is a key issue in understanding glass formation and plays a fundamental role in the development of advanced glass-ceramics. In the absence of catalyzing agents, most supercooled liquids crystallize heterogeneously from the external surfaces; only a few systems crystallize homogeneously in the interior. To gain further insight into the nucleation mechanism and the role of nucleating agents, it is essential to follow the formation of the first nuclei. An open issue about the early stages of nuclei formation in glasses is the following: which structural changes occur, especially in the local order around the network modifier cations (Na, Ca, Mg, Ba, etc.) and potential nucleating agents (Fe, Ti, Zr, etc.), during the pre-crystallization stage? ( when a glass is heat-treated for several hours at copious nucleation temperatures, but before significant crystallization takes place). Is the whole local structure around the cations modified well before crystallization is completed? The precise role of nucleating agents in glass-ceramic formation will likely only be understood by investigating the very first stages of crystallization with a strictly local structural probe having atomic selectivity. The X-ray Absorption Fine Structure (XAFS) technique is quite appropriate to characterize the local structure of specific cations present in glassy samples from the earliest stage of crystal nucleation. In this work, partially crystallized and fully crystallized samples were obtained after treatment at temperatures and times defined in previous studies. The XANES and EXAFS spectra of selected cations ions in the BaO-SiO2, Ba2TiSi2O7, CaMgSi2O6 – 9 mol% Fe2O3, MgO-SiO2, 1NaO-2CaO-3SiO2 and 2NaO-1CaO-3SiO2 glassy systems were collected at room temperature by using the transmission and total electron yield modes. A preliminary analysis of the data indeed showed modifications in the local order around some cations as the time of crystallization increased. The results will be fully discussed. (author)
[en] Intense intermittent radiation has been observed regularly in EAST plasmas. The duration of radiation bursts is with a characterization time of a few microseconds. The radiation is very intense, with an equivalent radiation temperature higher than the electron cyclotron emission by a few orders of magnitude. An electron density threshold exists to terminate the bursts, and it is strongly dependent on the toroidal magnetic field. The radiation frequency f is at the plasma frequency, and the frequency bandwidth is very narrow (∼1.5 MHz FWHM, ). The fine structure of the spectrum in the frequency domain has been observed, and the frequency spacing is around 3 MHz. The cavity modes model is capable of explaining the radiation frequency and the frequency spacing. However, a quantitative and complete description of this phenomenon is still lacking. (paper)
[en] Praseodymium (Pr) belongs to Lanthanide group; it has an unfilled f shell. Atomic Praseodymium is very rich in fine levels. Atomic structures both Pr I and Pr II have still not been completely classified. Few researchers have studied Pr fine structures theoretically. The 4f25d2 configuration of singly ionized Praseodymium (Pr II) has been investigated and term values, fine levels angular momenta and coupled wave functions arising from this configuration are being reported in this paper. To calculate the term values and wave functions, Russell-Saunders (L-S) and coefficient of fractional parentage methods have been used respectively. Spectroscopic terms for 4f25d2 configuration are 187, 457 J values of possible fine levels and 106 wave functions of given configuration have also been found. Wavefunctions could be used to calculate the energies of terms, transition probabilities, etc. (paper)
[en] Arsenic (As) contamination of surface and groundwater represents a serious environmental problem in many regions of Argentina. Geogenic As-contaminated waters are at equilibrium or slightly supersaturated with respect to calcite. This is the mechanism of formation of travertine rocks associated with carbonate and As-rich thermal waters in the Andean region. As rich carbonates also precipitate in soils of the Chaco-Pampean plain in the form of calcretes. As concentrations in the calcretes is ~10 ppm, while in travertines As concentrations are much higher (~3500 ppm). Regardless of their origin, these carbonates may play an important role in the mobility of As. Several scientific contributions are focused on the capacity of natural calcite to retain As-oxyanions. In the last decades, it was demonstrated that As-oxyanions may adsorb onto calcite surface and/or substitute the carbonate group, in the calcite structure. The aim of this study is to identify the As species in carbonates precpitated in different geologic environments associated with areas where high As concentrations have been reported in the water. X-ray absorption spectroscopy (XAS) was used to determine the oxidation state of As and their local chemical coordination. To carry out this study, three samples were analyzed: pedogenetic calcretes, geothermal and biogenic sediments were collected in the Chaco-Pampean and in the Puna region. XAS spectra were collected at the XAFS1 beamline at the Brazilian Synchrotron Light Laboratory (LNLS) in Campinas, Brazil. The XANES analysis allowed differentiating two oxidation states of As in the studied samples. As(V) is the dominant oxidation state (80-100%) while the As(III) represents less than 20% of the total As. EXAFS analysis indicate that As is mainly present in the form of As(V)-O species.Specifically, the proposed models resemble an arsenate-like structure, with the ~4 O atoms at a distance of ~1.68 Å around the As atom. The noisy EXAFS spetrum of the calcretes does not allow discriminating the second coordination shell; therefore, the obtained values can be adjusted to arsenate adsorbed onto either calcite or Fe(III)-(hydr)oxides. On the other hand, in geothermally and biogenically precipitated carbonates, the best EXAFS models suggest the presence of ~1 Fe atom at ~2.9 Å, ~2 Ca atoms at ~3.6 Å and ~2 Ca atoms at ~3.7 Å. The As-Fe shell is typical of arsenates adsorbed onto Fe(III)-(hydr)oxides, while the As-Ca shells are typical of arsenate substituting carbonate ions in the calcite structure. (author)
[en] We report on the experimental and theoretical interpretation of the diffraction of a probe beam during inscription of a surface relief grating with an interference pattern into a photo-responsive polymer film. For this, we developed a set-up allowing for the simultaneous recording of the diffraction efficiency (DE), the fine structure of the diffraction spot and the topographical changes, in situ and in real time while the film is irradiated. The time dependence of the DE, as the surface relief deepens, follows a Bessel function exhibiting maxima and minima. The size of the probe beam relative to the inscribed grating (i.e., to the size of the writing beams) matters and has to be considered for the interpretation of the DE signal. It is also at the origin of a fine structure within the diffraction spot where ring-shaped features appear once an irradiation time corresponding to the first maximum of the DE has been exceeded. Graphic abstract: .
[en] We consider a long range scalar force that mainly couples to dark matter and unstable Standard Model states, like the muon, with tiny strength. Probing this type of force would present a challenge to observations. We point out that the dependence of the induced background scalar field on dark matter number density can cause the mass of the unstable particles to have spatial and temporal variations. These variations, in turn, leave an imprint on the value of the fine structure constant α, through threshold corrections, that could be detected in astronomical and cosmological measurements. Our mechanism can accommodate the mild preference of the Planck data for such a deviation, . In this case, the requisite parameters typically imply that violations of Equivalence Principle may be within reach of future experiments.
[en] This paper is concerned with the investigation of the massless regime of an integrable spin chain based on the quantum group deformation of the superalgebra. The finite-size properties of the eigenspectra are computed by solving the respective Bethe ansatz equations for large system sizes allowing us to uncover the low-lying critical exponents. We present evidences that critical exponents appear to be built in terms of composites of anomalous dimensions of two Coulomb gases with distinct radii and the exponents associated to degrees of freedom. This view is supported by the fact that the XXZ integrable chain spectrum is present in some of the sectors of our superspin chain at a particular value of the deformation parameter. We find that the fine structure of finite-size effects is very rich for a typical anisotropic spin chain. In fact, we argue on the existence of a family of states with the same conformal dimension whose lattice degeneracies are apparently lifted by logarithmic corrections. On the other hand we also report on states of the spectrum whose finite-size corrections seem to be governed by a power law behaviour. We finally observe that under toroidal boundary conditions the ground state dependence on the twist angle has two distinct analytical structures.
[en] In this work, we have studied the quantum tunneling of a single spin–orbit-coupled atom held in a periodically modulated optical lattice with an impurity. As a result we find that the dynamical localization takes place globally at the collapse points of quasienergy spectrum, even when the impurity potential is far off-resonant with the driving field. Meanwhile, two types of local second-order tunneling processes appear beyond expectation between the two nearest-neighbor sites of the impurity, with the spin unchanged and with the impurity site population negligible. Though tunneling behaviors of the two types seem to be the same, they are believed to involve two distinct mechanisms: one is related to spin-independent process, while the other is to spin-dependent tunneling process. The two types of second-order processes can be identified by means of resonant tunneling with or without spin flipping by tuning the impurity potential to be in resonance with the driving field. In the Floquet picture, the system with the localized impurity develops a fine structure of avoided crossings of quasienergies near the collapse point, which is crucial to understand the so-called second-order tunneling dynamics. These results are confirmed analytically on the basis of effective three-site model and multiple-time-scale asymptotic perturbative method, and may be exploited for engineering the spin-dependent quantum transport in realistic experiments. (paper)