Splitting Of Spectral Lines Research Articles

Artificial neural network based autoregressive modeling technique with application in voice activity detection

A new method of estimating the coefficients of an autoregressive (AR) model using real-valued neural network (RVNN) technique is presented in this paper. The coefficients of the AR model are obtained from the synaptic weights and adaptive coefficients of the activation function of a two layer RVNN while the number of neurons in the hidden layer is estimated from over-constrained system of equations.The performance of the proposed technique has been evaluated using sinusoidal data and recorded speech so as to examine the spectral resolution and line splitting as well as its ability to detect voiced and unvoiced data section from a recorded speech. Results obtained show that the method can accurately resolve closely related frequencies without experiencing spectral line splitting as well as identify the voice and unvoiced segments in a recorded speech.

More on the circumbinary disk of SS 433

Certain lines in spectra of the Galactic microquasar SS 433, in particular the brilliant H alpha line, have been interpreted as emission from a circumbinary disk. In this interpretation the orbital speed of the glowing material is in excess of 200 km/s and the mass of the binary system in excess of 40 solar masses. A very simple model of excitation of disk material is in remarkable agreement with the observations, yet it seems that the very existence of a circumbinary disk is regarded as controversial. Published spectra, taken almost nightly over two orbital periods of the binary system, show H alpha and He I lines; these were analysed as superpositions of Gaussian components. A model in which the excitation of any given patch of putative circumbinary material is proportional to the inverse square of its instantaneous distance from the compact object was constructed and compared with observations. The new model provides an excellent description of the observations. The variation of the H alpha and He I spectra with orbital phase are described quantitatively provided the radius of the emitting ring is not much greater than the radius of the closest stable circumbinary orbit. The new analysis has greatly strengthened the case for a circumbinary disk orbiting the SS 433 system with a speed of over 200 km/s and presents supposed alternative explanations with major difficulties. If the circumbinary disk scenario is essentially correct, the mass of the binary system must exceed 40 solar masses and the compact object must be a rather massive black hole. The case is so strong that this possibility should be taken seriously.

Mid-IR Zeeman spectrum of nitric oxide molecules in a strong magnetic field

Nonlinear Zeeman splitting of ro-vibrational spectral lines of nitric oxide molecules in a variable magnetic field with maximum induction up to 6 T was studied both experimentally and theoretically. A single line frequency-tunable CO laser operating in the wavelength range of ∼5–6 µm was employed to detect absorption of its radiation by NO molecules versus time, i.e. to detect laser magnetic resonance (LMR) spectrograms. These LMR spectrograms were simulated with a numerical model in which Zeeman shifting of ro-vibrational energetic levels in the magnetic field was calculated with the perturbation theory of different orders. The observed LMR spectrograms appeared to be in adequate agreement with the numerical data calculated in the third order of the perturbation theory.

Least-squares deconvolution of the stellar intensity and polarization spectra

Least squares deconvolution (LSD) is a powerful method of extracting high-precision average line profiles from the stellar intensity and polarization spectra. Despite its common usage, the LSD method is poorly documented and has never been tested using realistic synthetic spectra. In this study we revisit the key assumptions of the LSD technique, clarify its numerical implementation, discuss possible improvements and give recommendations how to make LSD results understandable and reproducible. We also address the problem of interpretation of the moments and shapes of the LSD profiles in terms of physical parameters. We have developed an improved, multiprofile version of LSD and have extended the deconvolution procedure to linear polarization analysis taking into account anomalous Zeeman splitting of spectral lines. This code is applied to the theoretical Stokes parameter spectra. We test various methods of interpreting the mean profiles, investigating how coarse approximations of the multiline technique translate into errors of the derived parameters. We find that, generally, the Stokes parameter LSD profiles do not behave as a real spectral line with respect to the variation of magnetic field and elemental abundance. This problem is especially prominent for the Stokes I variation with abundance and Stokes Q variation with magnetic field. At the same time, the Stokes V LSD spectra closely resemble profile of a properly chosen synthetic line for the magnetic field strength up to 1 kG. We conclude that the usual method of interpreting the LSD profiles by assuming that they are equivalent to a real spectral line gives satisfactory results only in a limited parameter range and thus should be applied with caution. A more trustworthy approach is to abandon the single-line approximation of the average profiles and apply LSD consistently to observations and synthetic spectra.

Influence of pressure effect on Fermi resonance in binary solution

The Fermi resonance behaviours of the two groups of binary solutions — pyridine and methanol, benzene and carbon tetrachloride, under different pressures are investigated according to their Raman spectra. The effect of pressure on Fermi resonance in binary solution differs significantly from that in pure liquid. In a binary solution, with the intermolecular distance shortening, the intermolecular interaction potential increases, the shift rates of the Raman spectral lines increase, the spectral line splitting occurs ahead of that in pure liquid, and the wavenumber separation Δ0 between the unperturbed harmonic levels shifts more quickly, too. The Fermi resonance parameters, the coupling coefficient W and the intensity ratio R of the two Raman bands, decrease rapidly with pressure increasing, and the pressure at which Fermi resonance phenomenon disappears is much lower than that in pure liquid, especially in the solution whose molecules are of the same polarity. This article is valuable in the identification and the assignment of spectral lines under high pressure, as well as the study of high pressure effect, intermolecular interaction, and solvent effects in different cases, etc.

Modelling of mercury isotope separation in CP stellar atmospheres: Results and problems

Formation of anomalous isotope abundances in the atmospheres of chemically peculiar (CP) stars can be explained by light-induced drift (LID). This effect is additional to the radiative acceleration and appears due to systematic asymmetry of radiative flux in partly overlapping isotopic spectral line profiles. LID causes levitation of an isotope with a red-shifted spectral line and sinking of an isotope with a blue-shifted line, generating thus diffusive separation of isotopes. We have studied diffusion of mercury as a typical well-studied isotope-rich heavy metal. Our model computations show that in mercury-rich quiescent atmospheres of CP stars LID causes levitation of the heavier mercury isotopes and sinking of the lighter ones. Precise quantitative modelling of the process of isotope separation demands very high-resolution computations and the high-precision input data, including data on hyperfine and isotopic splitting of spectral lines, adequate line profiles and impact cross-sections. Presence of microturbulence and weak stellar winds can essentially reduce the effect of radiative-driven diffusion.

Observing and Modelling Stellar Magnetic Fields

In this chapter, we examine the question of how spectropo- larimetric observations of magnetic stars may be modelled, and how modelling techniques may be used to extract much detailed informa- tion about the stellar magnetic field and other characteristics of the magnetized stellar atmosphere. In the preceding chapter, we discussed how the energy levels of atoms are split by a magnetic field, and how this leads in turn to splitting of spectral lines in to multiple components, an effect called the Zeeman or Paschen-Back effect depending on the field strength. We saw that the polarisation characteristics of these components provide valuable tools for detection and measurement of stellar magnetic fields, and that polarisation measurements allow one to obtain, in a straight-forward way, an estimate of the mean line-of-sight field component averaged over the visible hemisphere (the mean longitudinal field h Bzi ). We also saw that, if the field is large enough and ve sin i small enough, observation of splitting of spectral lines into discrete components makes it possible to estimate the mean field modulus h Bi , again averaged over the visible hemisphere. Finally, we looked at some simple multipole models of stellar field structure that can reproduce simple data-sets such as observed values of h Bzi , or of h Bzi and h Bi , over a stellar rotation, and how these models lead to the fundamental conceptual model known as the oblique rotator. Determination of mean field values directly from the spectra (in the same way as radial velocities and projected rotation velocities are derived), and the modelling of such integral or moment data with simple geometric field structures, provide a useful and valuable source of information about global characteristics of the stellar field. However, such models are based on data-sets that are often

Microwave Spectrum, Conformation and Intramolecular Hydrogen Bonding of 2,2,2-Trifluoroethanethiol (CF3CH2SH)

The microwave spectrum of 2,2,2-trifluoroethanethiol, CF3CH2SH, and of one deuterated species, CF3CH2SD, has been investigated in the 7-80 GHz spectral interval. The microwave spectra of the ground and three vibrationally excited states belonging to three different normal modes of one conformer were assigned for the parent species, and the vibrational frequencies of these fundamentals were determined by relative intensity measurements. Only the ground vibrational state was assigned for the deuterated species. The identified form has a synclinal arrangement for the H-S-C-C chain of atoms and the corresponding dihedral angle is 68(5) degrees from synperiplanar (0 degrees). A weak intramolecular hydrogen bond formed between the thiol (SH) group and one of the fluorine atoms is stabilizing this conformer. There is no evidence in the microwave spectrum for the H-S-C-C antiperiplanar form. The hydrogen atom of the thiol group should have the ability to tunnel between two equivalent synclinal potential wells, but no splittings of spectral lines due to tunneling were observed. The microwave work was augmented by quantum chemical calculations at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVTZ levels of theory.

Model atmospheres of magnetic chemically peculiar stars

In the last few years we have developed stellar model atmospheres which included effects of anomalous abundances and strong magnetic field. The full treatment of anomalous Zeeman splitting and polarized radiative transfer were introduced in the model atmosphere calculations for the first time. In this investigation we present results of modelling the atmosphere of one of the most extreme magnetic chemically peculiar stars, HD137509. This Bp SiCrFe star has the mean surface magnetic field modulus of about 29kG. We use the recent version of the line-by-line opacity sampling stellar model atmosphere code LLmodels, which incorporates the full treatment of Zeeman splitting of spectral lines, detailed polarized radiative transfer and arbitrary abundances. We compare model predictions with photometric and spectroscopic observations of the star, aiming to reach a self-consistency between the abundance pattern derived from high-resolution spectra and abundances used for model atmosphere calculation. Based on magnetic model atmospheres, we redetermined abundances and fundamental parameters of HD137509 using spectroscopic and photometric observations. This allowed us to obtain a better agreement between observed and theoretical parameters compared to non-magnetic models with individual or scaled-solar abundances. We confirm that the magnetic field effects should be taken into account in the stellar parameter determination and abundance analysis.

LIF measurements on an atomic helium beam in the edge of a fusion plasma

A method for the absolute measurement of population densities of selected atomic helium levels, which has been applied on the tokamak TEXTOR at the Forschungszentrum Jülich in Germany, is presented. The method is based on the resonant excitation of selected levels by a high-power, narrow-band, pulsed laser beam saturating the optical pumping process. Observation of the fluorescence response is performed at the laser wavelength and elsewhere in the spectrum: this gives information on collisional population transfer between some excited levels. Data analysis, as required for the derivation of absolute population densities, includes due consideration of the Zeeman splitting of spectral lines in a strong magnetic field. The first results of the measured population densities are compared with those provided by simulation based on the collisional–radiative model for atomic helium in the edge of fusion plasmas. This code has been extended to include the laser interaction with atomic helium, in order to simulate the measured time traces of radiation from the laser-perturbed levels. A combination of this simulation procedure with laser-induced fluorescence measurements is suggested as a possible method for determining the electron density in the edge plasma.

Tunnelling time and tunnelling dynamics

The concept of ‘tunnelling time’ in the context of quantum particle tunnelling is reviewed. Various suggestions of linking the tunnelling dynamics with a characteristic time (real or complex) like the phase time, barrier interaction time (bounce time), presence time, etc. are analysed. A simple but fully quantal method of defining and estimating a real tunnelling time is examined in a variety of situations. The recently proposed idea of interpreting ‘tunnelling time’ as the cavity lifetime of a particle is also explored. We emphasize that proton or H-atom transfer reactions in double or triple wells offer systems in which the signature of the tunnelling time should be recognizable not just indirectly through the tunnelling splitting of spectral lines, but by following the relaxation dynamics of the subsystem that the proton or H atom leaves by tunnelling.

Nuclear quadrupole resonance in the gamma-resonance spectra of soft matter

It is shown that the harmonic librations (oscillations) of the principal axis of the electric field gradient tensor in “cages” of liquids, glasses, ferroliquids, and other “soft” systems qualitatively change the shape of the Mossbauer spectra of the quadrupole hyperfine structure. In addition to an effective decrease in the quadrupole coupling constant in the fast-libration limit, nuclear quadrupole resonance is predicted, which must be manifested in the Mossbauer spectra at the libration frequency that is approximately equal to the quadrupole splitting of spectral lines. By analogy with nuclear magnetic resonance, simple analytical expressions are derived, which describe resonance Mossbauer spectra in terms of the effective quadrupole coupling constant and the resonance splitting constant for the main lines. The observed features of the formation of quadrupole hyperfine structure spectra can be manifested in the Mossbauer spectra of soft matter and must be taken into account in analysis of experimental data.

Doppler-Free Two-Photon Spectroscopy of 6S1/2–6D3/2,5/2Transition in Cesium

The Doppler-free two-photon spectra of the 6 S 1/2 ( F = 3)–6 D 3/2 ( F = 2 to 5), 6 S 1/2 ( F = 4)–6 D 3/2 ( F = 2 to 5), 6 S 1/2 ( F = 3)–6 D 5/2 ( F = 5 to 1) and 6 S 1/2 ( F = 4)–6 D 5/2 ( F = 6 to 2) transitions in cesium are observed using a titanium-sapphire laser. These spectra can be used as an optical frequency standard. The hyperfine coupling constants A (magnetic dipole constant) and B (electric quadrupole constant) are determined using spectral line splittings, giving A = 16.17(17) MHz and B = 0.11(127) MHz for the 6 D 3/2 state, and A =-4.56(9) MHz and B = -0.35(183) MHz for the 6 D 5/2 state.

The Regularities of the Dynamic Stark Effect in Rare Gases

The regularities of the dynamic Stark effect in a high-frequency discharge in rare gases as well as the regularities observed under shift and splitting of spectral lines in the electric field for helium, neon, argon, and krypton are studied theoretically. The Schrodinger equation is solved by the diagonalization of the atomic-energy matrix in the electric field within the rotating-wave approximation.

Asteroseismic determination of stellar angular momentum

The total angular momentum of stars is an important diagnostic for testing theories of formation of stars. Angular momentum can also play a decisive role in the evolution of stars, in particular towards the higher masses. Asteroseismology can play an important role in providing measurement of this parameter. The spectrum of stellar oscillations is affected by rotation in a way similar to the splitting of spectral lines through the magnetic Zeeman effect. It is shown here that this can be used to determine accurately the total angular momentum of stars, taking full differential rotation into account, and without any dependence of inclination angle of rotation axis with respect to the line of sight. All aspects of this technique are addressed, including the issue of mode identification, determination of the moment of inertia, and the influence of the reference model on the seismic inference. It is a realistic prospect to do asteroseismogyrometry with planned space satellite missions such as MOST, MONS, COROT, and Eddington.

Effects of nonlocality in time of interactions of an atom with its surroundings on the broadening of spectral lines of atoms

We investigate effects of nonlocality in time of the interaction of an atom with its surroundings on the spectral line broadening. We show that these effects can be very significant: in some cases nonlocality in time of this interaction can give rise to a spectral line splitting.

Calcium niobium gallium and calcium lithium niobium gallium garnets doped with rare earth ions––effective laser media

The results of spectroscopy and laser action of disordered calcium niobium gallium (CNGG) and calcium lithium niobium gallium (CLNGG) garnets doped with Nd3+, Eu3+, Er3+, Ho3+ and Tm3+ were displayed. The structure and some optical and physical properties of CNGG and CLNGG-crystals were studied. Activator centers construction and the mechanism of inhomogeneous broadening and splitting of spectral lines of rare earth ions (TR3+) in CNGG and CLNGG-crystals were analyzed. Possibilities of laser media based on CNGG and CLNGG with TR3+-ions for pulse free running, Q-switch, CW and ultrashort pulse operation regimes were considered.

Ultrahigh magnetic field diagnostic with spectral profile calculation

We report the theoretical results on use of neon as a tracer element to measure the multi-megagauss magnetic field, which is induced in the ultrahigh intense laser–matter interactions. The shape of Zeeman splitting of spectral line for 1s2p( 1P 1)→1s 2 transition of He-like neon are calculated for high-intensity laser produced quasi one-components plasma with the consideration of the electron collision broadening, electron collision shift and magnetic field splitting. The results show that all of the Zeeman splitting spectrum can be identified under Rayleigh criterion for the plasma with the electron temperature from 10 to 100 eV , the magnetic field from 10 6 to 10 8 G and the electron density 2×10 20 cm −3 . With both the electron temperature and magnetic field increasing, the requirement for the resolution power of the spectrometer decreases. If a spectrometer with the resolution power of 1/1000 is used, the measurement of the quasistatic magnetic field by Zeeman splitting of spectral lines is applicable when quasistatic magnetic field is larger than some tens of megaGauss.

Neutron Capture Elements ins‐Process–Rich, Very Metal‐Poor Stars

We report abundance estimates for neutron capture elements, including lead (Pb), and nucleosynthesis models for their origin, in two carbon-rich, very metal-poor stars, LP 625-44 and LP 706-7. These stars are subgiants whose surface abundances are likely to have been strongly affected by mass transfer from companion asymptotic giant branch (AGB) stars that have since evolved to white dwarfs. The detections of Pb, which forms the final abundance peak of the s-process, enable a comparison of the abundance patterns from Sr (Z = 38) to Pb (Z = 82) with predictions of AGB models. The derived chemical compositions provide strong constraints on the AGB stellar models, as well as on s-process nucleosynthesis at low metallicity. The present paper reports details of the abundance analysis for 16 neutron capture elements in LP 625-44, including the effects of hyperfine splitting and isotope shifts of spectral lines for some elements. A Pb abundance is also derived for LP 706-7 by a reanalysis of a previously observed spectrum. We investigate the characteristics of the nucleosynthesis pathway that produces the abundance ratios of these objects using a parametric model of the s-process without adopting any specific stellar model. The neutron exposure τ is estimated to be about 0.7 mbarn-1, significantly larger than that which best fits solar system material, but consistent with the values predicted by models of moderately metal-poor AGB stars. This value is strictly limited by the Pb abundance, in addition to those of Sr and Ba. We also find that the observed abundance pattern can be explained by a few recurrent neutron exposures and that the overlap of the material that is processed in two subsequent exposures is small (the overlap factor r ~ 0.1).

Dynamics of multiply charged ions in intense laser fields

We numerically investigate the dynamics of multiply charged hydrogenic ions in near-optical linearly polarized laser fields with intensities of order ${10}^{16}--{10}^{17}{\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}.$ The weakly relativistic interaction is appropriately described by the Hamiltonian arising from the expansion of the Dirac equation up to the second order in the ratio of the electron velocity $v$ and the speed of light c. Depending on the charge state Z of the ion, the relation of strength between laser field and ionic core changes. We find around $Z=12,$ typical multiphoton dynamics and for $Z=3$ tunneling behavior, however, with clear relativistic signatures. In first order in $v/c$ the magnetic field component of the laser field induces a Z dependent drift in the laser propagation direction and a substantial Z dependent angular momentum with repect to the ionic core. While spin oscillations occur already in first order in $v/c$ as described by the Pauli equation, spin induced forces via spin-orbit coupling only appear in the parameter regime where ${(v/c)}^{2}$ corrections are significant. In this regime for $Z=12$ ions, we show strong splittings of resonant spectral lines due to spin-orbit coupling and substantial corrections to the conventional Stark shift due to the relativistic mass shift while those to the Darwin term are shown to be small. For smaller charges or higher laser intensities, parts of the electronic wave packet may tunnel through the potential barrier of the ionic core and when recombining, are shown to give rise to keV harmonics in the radiation spectrum. Some parts of the wave packet do not recombine after ionization and we find very energetic electrons in the weakly relativistic regime of above threshold ionization.