Sergej A. Choroszavin ( sergius@pve.vsu.ru )
 The Ground, a String, Two Elastic Springs.
 Simple Exactly Solvable Models
 of One-Dimensional Scalar Fields 
 with Concentrated Factors. 
(50K, LaTeX 2.09)

ABSTRACT.   This paper is an electronic application to my set of lectures, 
 subject:`Formal methods in solving differential equations and 
 constructing models of physical phenomena'. Addressed, mainly: 
 postgraduates and related readers. 
 Content: 
 a discussion of the simple models
 ( I would rather say, toy models )
 of the interaction based 
 on equation arrays of the kind: 
 d^2 u(t,x)/dt^2=c^{2}d^2 u(t,x)/dx^2
                 -4{\gamma_a}c\delta(x-x_a) Q_a(t)
                 -4{\gamma_b}c\delta(x-x_b) Q_b(t), 
 Q_a(t) = u(t,x_a),  Q_b(t) = u(t,x_b).
 Central mathematical points: d'Alembert-Kirchhoff-like Formulae,
 Finite Rank Perturbations.