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Oscillations of first-order delay differential equations in a critical state. (English) Zbl 0882.34069
The first-order delay differential equation $x'(t)+a(t)x(t-\tau)=0, \qquad \tau>0,\quad t\geq t_0,$ is considered. It has been shown by Myshkis that in the case if $$a(t)\geq0$$ and $$\liminf_{t\to\infty} a(t)>{1/(\tau e)}$$ all solutions oscillate.
Yu. Domshlak [Funct. Differ. Equ. 2, 59-68 (1994; Zbl 0860.34036)] observed in a previous work that there exist equations of this type with $$\liminf_{t\to\infty} a(t)={1/(\tau e)}$$ (critical case) such that all their solutions are oscillatory in spite of the fact that the corresponding limiting equation $$x'(t)+{1\over\tau e}x(t-\tau)=0$$ admits the nonoscillatory solution $$x(t)=\exp(-{t\over\tau})$$.
In the present paper it is shown that for the arisal of such a situation it suffices that additionally the following equalities are satisfied $\liminf_{t\to\infty}\left[\left(a(t)-{1\over\tau e}t^2 \right)\right]= {\tau\over 8e},\qquad \liminf_{t\to\infty}\left[\left(a(t)-{1\over\tau e}t^2 -{\tau\over 8e} \right)\right]> -{\tau\over 8e}.$
Reviewer: I.Ginchev (Varna)

##### MSC:
 34K11 Oscillation theory of functional-differential equations 34C10 Oscillation theory, zeros, disconjugacy and comparison theory for ordinary differential equations
##### Keywords:
delay differential equations; oscillations
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##### References:
 [1] Domshlak Y., Sturmian Comparison Method in investigation of the be-havior. of solutions for Differential-Operator Equations. (1986) [2] Domshalk Y., Functional Differential Equational. Israe-Seminar 2 pp 59– [3] Elbert A., Recent trends in differential equations. World Sci. Ser. Appl. Anal. World Sci. Publishing co. 1 pp 163– (1992) [4] Elbert A., T. R. N{$$\deg$$}0. 228 Proc. Amer. Math. Soc. 128 pp 1503– (1995) [5] Hille E., Trans. Amer. Math. Sco. 64 pp 234– (1948) [6] Kneser A., Math. Ann. 42 pp 409– (1893) · JFM 25.0522.01 [7] Koplatadze R. G., Differential Uravnenija ’nye 18 pp 1463– (1982)
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