1. Geometric Optics for the Nonlinear Systems of Kirchhoff-type, Preprint 2001/22, ISSN 1437-739X, Institut für Mathematik, Universität Potsdam,  2001.

2.  K. Kajitani, S. Wakabayashi, and K.Yagdjian: The C-infinity-well posed Cauchy problem for hyperbolic operators  with multiple characteristics
    vanishing with the different speeds, Mathematical Research Note, Institute of Mathematics, University of Tsukuba, 2000-005, March, 2000.

3. H. Ishida, K.Yagdjian: On a precise Levi condition in Gevrey classes for some   infinitely degenerate hyperbolic equations and its necessity,
    Mathematical Research Note, Institute of Mathematics, University of Tsukuba, 2000-006, March, 20000

                                                                                                                       1999

4. Parametric resonance and nonexistence of  global solution  to nonlinear wave equations,  Mathematical Research Note,
     Institute of Mathematics, University of Tsukuba, 99-001, March, 1999.

5. The Lax-Mizohata theorem for nonlinear gauge invariant equations,  Mathematical Research Note, Institute of Mathematics,
     University of Tsukuba, 99-002, March, 1999.

6.  The Lax-Mizohata theorem for the Kirchhoff type equations,  Mathematical Research Note, Institute of Mathematics,
      University of Tsukuba, 99-006, September, 1999.

7.M.Reissig ,  K.Yagdjian: Klein-Gordon type decay rates for wave equations with time-dependent coefficients,  Mathematical Research Note,
      Institute of Mathematics, University of Tsukuba, 99-008, October, 1999.

                                                                                                                      1998
8.  M.Reissig, K.Yagdjian : Lp -Lq estimates for the solutions of strictly hyperbolic equations of second order with time dependent coefficients
     -Oscillations via growth- Technische Universitat Bergakademie Freiberg, Preprint 98-5.

9. A.A.Galstian , K.Yagdjian : Exponential Function of Pseudo-Differential Operators, Arbeitsgruppe ``Partielle Differentialgleichungen und Komplexe
     Analysis'', Institut für Mathematik, Universität Potsdam, Preprint 97/13, May, 1997.

10. M.Reissig , K.Yagdjian : Weakly hyperbolic equations with fast oscillating coefficients, Technische Universitat Bergakademie Freiberg, Preprint 97-07.

11. Introduction to Theory of Fourier Integral Operators with Applications to Weakly Hyperbolic Equations, Institute of Mathematics, University of
     Tsukuba,   96-006, June, 1996.

12. M.Reissig , K.Yagdjian : On the Stokes matrix for a family of infinitely degenerate operators of second order, Technische Universitat Bergakademie Freiberg,      Preprint 95-04.

13. JWKB Representation for equations with infinite order turning point, Max-Planck-Institute för Mathematik, Bonn, MPI/95-66.
 

14. M.Reissig , K.Yagdjian : On the Cauchy problem for quasilinear weakly hyperbolic equations with time degeneration, Technische Universitat Bergakademie   Freiberg, Preprint 93-04.

15. Necessary conditions for the correctness of the Cauchy problem for operators with multiple characteristics, Mathematical Department University of Pisa, 2.132(709) November.

16. Representation theorem for the solution of the equations with the turning point of infinite order, Mathematical Department University of Pisa,   2.133(711)  November.