Semi-quantitative Models Research Articles

Gravitational and doppler redshifts of quasars interpreted as massive black holes ejected from galaxies

This is a first attempt to find a realistic explanation of the observed redshifts of quasars associated with galaxies, by considering, in addition to the inertial, also the gravitational time dilation in the strong field of quasars interpreted as huge black holes accreting matter from their surroundings. This interpretation allows us to understand the observed predominance of excess redshifts of quasars and construct possible semiquantitative models for the pair NGC 4319/Markarian 205. The proposed models do not contradict to the present astrophysical knowledge, but a selection of the most satisfactory one is still difficult because of the existing uncertainty in estimates of the sizes of radiating regions in matter accreted by a flying black hole.

On the theory of spectral line broadening : vibrational dephasing and resonance energy transfer in molecular liquids

Starting from a microscopic description a theory is presented which investigates the vibrational line-broadening mechanisms in dense molecular fluids. The paper consists of two parts. (i) Within the Zwanzig-Mori representation of the vibrational correlation functions, a formalism is developed which allows a unified and systematic description of the various line-broadening processes (pure dephasing, vibrational relaxation, resonant and non-resonant vibrational transfer) within the concepts of liquid-state theory. It is found that the vibrational linewidth cannot be represented as a sum of individual linewidths related to these particular mechanisms. (ii) Including only quasi-elastic processes (i.e. transition frequency modulations and vibrational resonance transfer), semiquantitative models are presented which describe the explicit time behaviour (in particular the exponential decay time of the vibrational correlation function. By means of a simplified interaction model we obtain numerical estimates for th...

Swelling effects of electromagnetic waves near the critical density

Numerical techniques have been used to study the intensity pattern of a high-frequency electromagnetic wave near the critical density for conditions typical of laser fusion plasmas. The investigation considered nonlinear density profiles, collisional absorption, and finite bandwidth effects. Using the results of these calculations as a guide, elementary analytic models were developed to describe the behavior of the intensity pattern. Results of the numerical and analytic methods indicate the following: (i) For a nonlinear but monotonic density profile, the swelling factor can be related to the Airy function pattern by a simple scale factor; (ii) for collisional absorption below 50%, a linear relation holds between the intensity and the absorption; (iii) for laser bandwidth Δω/ω0<15%, the intensity is reduced in a manner similar to that associated with collisional absorption. Within the ranges given, accuracy of the analytic models is within 10% of the numerical results. These semiquantitative models provide simple, useful tools for estimating the intensity patterns near the critical density.