Geodesic
The spectrum of an elliptic operator of second order
Matematičeskie zametki, Tome 20 (1976) no. 3, pp. 351-358.

Voir la notice de l'article provenant de la source Math-Net.Ru

Under minimal requirements on the coefficients and the boundary of the domain it is proved that the spectrum of the first boundary-value problem for an elliptic operator of second order always lies in the half-plane $\lambda'\le\operatorname{Re}\lambda$, where $\lambda'$ is the leading eigenvalue to which there corresponds a nonnegative eigenfunction. On the line $\operatorname{Re}\lambda=\lambda'$, there are no other points of the spectrum. 
@article{MZM_1976_20_3_a5,
     author = {T. M. Kerimov and V. A. Kondrat'ev},
     title = {The spectrum of an elliptic operator of second order},
     journal = {Matemati\v{c}eskie zametki},
     pages = {351--358},
     publisher = {mathdoc},
     volume = {20},
     number = {3},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1976_20_3_a5/}
}
TY  - JOUR
AU  - T. M. Kerimov
AU  - V. A. Kondrat'ev
TI  - The spectrum of an elliptic operator of second order
JO  - Matematičeskie zametki
PY  - 1976
SP  - 351
EP  - 358
VL  - 20
IS  - 3
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/MZM_1976_20_3_a5/
LA  - ru
ID  - MZM_1976_20_3_a5
ER  - 
%0 Journal Article
%A T. M. Kerimov
%A V. A. Kondrat'ev
%T The spectrum of an elliptic operator of second order
%J Matematičeskie zametki
%D 1976
%P 351-358
%V 20
%N 3
%I mathdoc
%U http://geodesic.mathdoc.fr/item/MZM_1976_20_3_a5/
%G ru
%F MZM_1976_20_3_a5
T. M. Kerimov; V. A. Kondrat'ev. The spectrum of an elliptic operator of second order. Matematičeskie zametki, Tome 20 (1976) no. 3, pp. 351-358. http://geodesic.mathdoc.fr/item/MZM_1976_20_3_a5/