Spectroscopic studies of premixed laminar flames

A critical review is presented of the results obtained by spectroscopic observations on flames. The objective of the survey is to examine the status, promise, and deficiencies of combustion spectroscopy in its relation to (a) elucidation of the mechanism of combustion and (b) the solution of technical combustion problems. Since important spectroscopic studies have been carried out on low-pressure flames, a discussion of the probable effects of pressure on laminar flame propagation is also included

Spectroscopic studies of fluorescent perylene dyes

The lowest electronic transition of the fluorescent perylene dye bis-(3,5-di-tertbutylphenyl)-perylene-3, 4:9,10-biscarboximide has been investigated

Spectroscopic studies in open quantum systems

The spectroscopic properties of an open quantum system are determined by the eigenvalues and eigenfunctions of an effective Hamiltonian H consisting of the Hamiltonian H_0 of the corresponding closed system and a non-Hermitian correction term W arising from the interaction via the continuum of decay channels. The eigenvalues E_R of H are complex. They are the poles of the S-matrix and provide both the energies and widths of the states. We illustrate the interplay between Re(H) and Im(H) by means of the different interference phenomena between two neighboured resonance states. Level repulsion along the real axis appears if the interaction is caused mainly by Re(H) while a bifurcation of the widths appears if the interaction occurs mainly due to Im(H). We then calculate the poles of the S-matrix and the corresponding wavefunctions for a rectangular microwave resonator with a scatter as a function of the area of the resonator as well as of the degree of opening to a guide. The calculations are performed by using the method of exterior complex scaling. Re(W) and Im(W) cause changes in the structure of the wavefunctions which are permanent, as a rule. At full opening to the lead, short-lived collective states are formed together with long-lived trapped states. The wavefunctions of the short-lived states at full opening to the lead are very different from those at small opening. The resonance picture obtained from the microwave resonator shows all the characteristic features known from the study of many-body systems in spite of the absence of two-body forces. The poles of the S-matrix determine the conductance of the resonator. Effects arising from the interplay between resonance trapping and level repulsion along the real axis are not involved in the statistical theory.Comment: The six jpg files are not included in the tex-fil

Infra-red Spectroscopic Studies of GdBaCo2O5.5

This paper reports infrared spectroscopic studies on GdBaCo$_{2}$O$_{5.5}$ layered perovskite which exhibits successive magnetic transitions from paramagnetic to ferromagnetic to antiferromagnetic states as well as high temperature metal to insulator transition and a change in charge transport mechanism at low temperature. Infrared absorption spectra recorded at various temperatures in the range 80 K to 350 K reveal changes in the positions of Co-O stretching and bending frequencies which provide an explanation to the magnetic and transport behaviour of this compound.Comment: 5 figure

Spectroscopic Fingerprint of Phase-Incoherent Superconductivity in the Cuprate Pseudogap State

A possible explanation for the existence of the cuprate "pseudogap" state is that it is a d-wave superconductor without quantum phase rigidity. Transport and thermodynamic studies provide compelling evidence that supports this proposal, but few spectroscopic explorations of it have been made. One spectroscopic signature of d-wave superconductivity is the particle-hole symmetric "octet" of dispersive Bogoliubov quasiparticle interference modulations. Here we report on this octet's evolution from low temperatures to well into the underdoped pseudogap regime. No pronounced changes occur in the octet phenomenology at the superconductor's critical temperature Tc, and it survives up to at least temperature T ~ 1.5Tc. In the pseudogap regime, we observe the detailed phenomenology that was theoretically predicted for quasiparticle interference in a phase-incoherent d-wave superconductor. Thus, our results not only provide spectroscopic evidence to confirm and extend the transport and thermodynamics studies, but they also open the way for spectroscopic explorations of phase fluctuation rates, their effects on the Fermi arc, and the fundamental source of the phase fluctuations that suppress superconductivity in underdoped cuprates.Comment: 27 pages, 12 figure

Spectroscopic studies of Dy-168,170 using CLARA and PRISMA

Preliminary results from an experiment aiming at Dy-170. Submitted to the LNL Annual Report 2008.Comment: 2 pages, 4 figures, Submitted to the LNL Annual Report 200

Effects of dust absorption on spectroscopic studies of turbulence

We study the effect of dust absorption on the recovery velocity and density spectra as well as on the anisotropies of magnetohydrodynamic turbulence using the Velocity Channel Analysis (VCA), Velocity Coordinate Spectrum (VCS) and Velocity Centroids. The dust limits volume up to an optical depth of unity. We show that in the case of the emissivity proportional to the density of emitters, the effects of random density get suppressed for strong dust absorption intensity variations arise from the velocity fluctuations only. However, for the emissivity proportional to squared density, both density and velocity fluctuations affect the observed intensities. We predict a new asymptotic regime for the spectrum of fluctuations for large scales exceeding the physical depths to unit optical depth. The spectrum gets shallower by unity in this regime. In addition, the dust absorption removes the degeneracy resulted in the universal $K^{-3}$ spectrum of intensity fluctuations of self-absorbing medium reported by Lazarian \& Pogosyan. We show that the predicted result is consistent with the available HII region emission data. We find that for sub-Alfv\'enic and trans-Alfv\'enic turbulence one can get the information about both the magnetic field direction and the fundamental Alfv\'en, fast and slow modes that constitute MHD turbulence.Comment: Published in MNRAS, minor changes to match the published versio