Abstract
In this work, we obtain necessary and sufficient conditions for the oscillation of the solutions to a second-order neutral differential equation with mixed delays. Two examples are provided to show effectiveness and feasibility of main results. Our main tool is the Lebesgue’s Dominated Convergence theorem.
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1 Introduction
In this paper, we are interested in the study of certain oscillation properties of second-order differential equations containing mixed several delays.
Nowadays, the study of qualitative properties of ordinary differential equations attracts considerable attention from the scientific community due to numerous applications of them to several contexts, such as Biology, Physics, Chemistry, and Dynamical Systems. For some details related to the recent studies on oscillation and non-oscillation properties, exponential stability, instability, existence of unbounded solutions of the equations under consideration, we refer the reader to the books [1, 2].
It is worthy pointing out that both oscillation and stability criteria are currently used in the studies of non-linear mathematical models with delay for single species and several species with interactions, in logistic models, \(\alpha \)-delay models, mathematical models with varying capacity, mathematical models for food-limited population dynamics with periodic coefficients, and diffusive logistic models (for instance, diffusive Malthus-type models with several delays, autonomous diffusive delayed logistic models with Neumann boundary conditions, periodic diffusive logistic Volterra-type models with delays, and so on).
The literature is full of very interesting results related to the oscillation properties for second-order differential equations. Now, we recall some studies that possess a strong connection with the content of this paper. In [3], Baculíková, Li, and Džurina obtained some oscillation criteria for the following second-order neutral differential equations:
considering the cases in which the arguments are delayed, advanced, or mixed.
In [4], Arul and Shobha investigated some oscillation properties of the solutions of the following equation:
being \(z(t)=u(t)+a(t)u(t-\tau )+b(t)u(t+\delta )\).
In [5], Thandapani and Rama considered the second-order non-linear neutral differential equations of mixed type. Precisely, the authors studied the following neutral differential equations:
being \(\alpha \) and \(\beta \ge 1\) defined as the ratios of odd positive integers. Some generalizations of the results discussed in [5] are contained in [6].
More general results are contained in [7] where Thandapani, Padmavathi, and Pinelas derived oscillation theorems for even-order non-linear neutral differential equations with mixed type with the following form:
being \(t\ge t_0\), \(n\ge 2\) an even integer, \(\alpha \ge 1\) and \(\beta \ge 1\) ratios of odd positive integers. The case in which n is odd was treated for slightly different equations in [8, 9].
It is interesting to notice that in the aforementioned works, the authors obtained only sufficient conditions that ensure the oscillation of the solutions of the considered equations. A problem worthy of investigations is the study of necessary and sufficient conditions for the oscillation and some satisfactory answers were given in [10, 13].
Finally, we refer the interested reader to the following paper and to the references therein for some recent results on the oscillation theory for ordinary differential equations of several orders [11,12,13,14,15,16,17,18].
In this work, we deal with necessary and sufficient conditions for the oscillation of solutions to a second-order non-linear differential equations of the form
where
being the functions \(g_j, r_j,p,q,\nu _j,\varsigma \) continuous and such that the following conditions stated below hold:
-
(a)
\(\nu _j\in C([0,\infty ),{\mathbb {R}})\), \(\varsigma \in C^2([0,\infty ),{\mathbb {R}})\), if we consider the simple delay, then \(\nu _j(t)<t\), \(\varsigma (t)<t\), \(\lim _{t\rightarrow \infty }\nu _j(t)=\infty \), \(\lim _{t\rightarrow \infty }\varsigma (t)=\infty \);
-
(b)
\(\nu _j\in C([0,\infty ),{\mathbb {R}})\), \(\varsigma \in C^2([0,\infty ),{\mathbb {R}})\), if we consider the advanced delay, then (a) can be modified by \(\nu _j(t)>t\), \(\varsigma (t)<t\), \(\lim _{t\rightarrow \infty }\nu _j(t)=\infty \), \(\lim _{t\rightarrow \infty }\varsigma (t)=\infty \);
-
(c)
\(p\in C^1([0,\infty ),{\mathbb {R}})\), \(r_j\in C([0,\infty ),{\mathbb {R}})\); \(0<p(t)\), \(0\le r_j(t)\) for all \(t \ge 0\) and \(j=1,2,\dots ,m\); \(\sum r_j(t)\) is not identically zero in any interval \([b,\infty )\);
-
(d)
\(q\in C^2([0,\infty ),{{\mathbb {R}}_+})\) with \(0\le q(t)\le a<1\);
-
(e)
\(g_j \in C({\mathbb {R}},{\mathbb {R}})\) is non-decreasing and \(g_j(t)t>0\) for \(t\ne 0\), \(j=1,2,\dots ,m\);
-
(f)
\(\lim _{t\rightarrow \infty }P(t)=\infty \) where \(P(t)=\int _0^t p^{-1/\alpha }(s)\,\mathrm{d}s\);
-
(g)
\(\alpha \) is the quotient of two positive odd integers.
For the sake of completeness, we recall some basic definitions. A solution of (1.1) is a function \(u: [t_u,\infty [\rightarrow {\mathbb {R}}\), \(t_u\ge t_0\), such that \(p(t)\big (w'(t)\big )^\alpha \) and u(t) are continuously differentiable for all \(t \in [t_u,\infty [\) and it satisfies (1.1) for all \(t\in [t_u,\infty [\). A solution u(t) of (1.1) is said to be non-oscillatory if it is eventually positive or eventually negative; otherwise, it is said to be oscillatory. Finally, we say that (1.1) is oscillatory if all of its solutions are oscillatory.
2 Preliminary results
For the sake of simplicity, we set
Lemma 2.1
Suppose that (a)–(g) hold for \(t \ge t_0\) and that u is an eventually positive solution of (1.1). Then, w satisfies
Proof
Let u be an eventually positive solution. Then, \(w(t)>0\) and there exists \(t_0\ge 0\), such that \(u(t)>0\), \(u(\nu _j(t))>0\), \(u(\varsigma (t))>0\) for all \(t \ge t_0\) and \(j=1,2,\dots ,m\). Then, (1.1) gives that
which shows that \(p(t)\big (w'(t)\big )^\alpha \) is non-increasing for \(t \ge t_0\). Next, we claim that \(p(t)\big (w'(t)\big )^\alpha \) is positive for \(t \ge t_1>t_0\). If not, there exists a point \(t \ge t_1>t_0\), such that \(p(t)\big (w'(t)\big )^\alpha \le 0\). Therefore, we can choose \(c>0\), such that
that is
Integrating both sides from \(t_1\) to t, we get
Taking the limit of both sides as \(t\rightarrow \infty \), we have \(\lim _{t\rightarrow \infty }w(t)\le -\infty \) which leads to a contradiction to \(w(t)>0\). Hence, \(p(t)\big (w'(t)\big )^\alpha >0\) for \(t \ge t_1\), that is, \(w'(t)>0\) for \(t \ge t_1\). This completes the proof. \(\square \)
Lemma 2.2
Suppose that (a)–(g) hold for \(t \ge t_0\) and that u is an eventually positive solution of (1.1). Then, w satisfies
Proof
Assume that u be an eventually positive solution of (1.1). Then, \(w(t)>0\) and there exists \(t \ge t_1>t_0\), such that
Hence, w satisfies (2.3) for \(t \ge t_1\). \(\square \)
3 Main results
In Theorem 3.1, we use a constant \(\beta \), quotient of two odd positive integers with \(\beta >\alpha \), for which
Existence of such constant can be established by taking \(g_j(t)=|y|^\delta {\text {sgn}}(t)\), with \(\beta <\delta \).
Theorem 3.1
Let (b)–(g) and (3.1) for \(t \ge t_0\). Then, every solution of (1.1) is oscillatory if and only if
Proof
Let u is an eventually positive solution of (1.1). Then, \(w(t)>0\) and there exists \(t_0\ge 0\), such that \(u(t)>0\), \(u(\nu _j(t))>0\), \(u(\varsigma (t))>0\) for all \(t \ge t_0\) and \(j=1,2,\dots ,m\). Thus, Lemmas 2.1 and 2.2 hold for \(t \ge t_1\). By Lemma 2.1, there exists \(t_2>t_1\), such that \(w'(t)>0\) for all \(t \ge t_2\). Then, there exist \(t_3>t_2\) and \(c>0\), such that \(w(t)\ge c\) for all \(t \ge t_3\). Next, using Lemma 2.2, we wet \(u(t)\ge (1-a)w(t)\) for all \(t \ge t_3\) and (1.1) become
Integrating (3.3) from t to \(\infty \), we get
Since \(p(t)\big (w'(t)\big )^\alpha \) is positive and non-decreasing \(\lim _{t\rightarrow \infty } p(t)\big (w'(t)\big )^\alpha \) finitely exists and positive
that is
Since
Then, we use (3.5) in (3.4) to get
Next, if we set \(K=\frac{g_0[c(1-a)]}{c^\beta }\) where \( g_0[c(1-a)]= \min _{1\le j\le m} g_j[c(1-a)]\), the above inequality becomes
Using (b) and w(t) is non-decreasing, we have
that is
Integrating both sides from \(t_3\) to \(\infty \), we get
due to \(\beta >\alpha \), which is a contradiction to (3.2), and hence, the sufficiency part of the theorem is proved.
Next, we prove necessary part reasoning by contradiction. If (3.2) does not hold, then for every \(\varepsilon >0\), there exists \(t \ge t_0\) for which
where \(2\varepsilon =\left[ \max _{\{1\le j\le m\}} g_j(\frac{1}{1-a})\right] ^{-1/\alpha }>0\).
Let us define the set
and \(\Phi : V\rightarrow V\) as
Now we prove that \((\Phi u)(t)\in V\). For \(u(t) \in V\), we have
and furthermore, for \(u(t)\in V\),
Hence, \(\Phi \) maps from V to V. Now, we find a fixed point for \(\Phi \) in V which will give an eventually positive solution of (1.1). To this end, we define a sequence of functions in V by
We have \(u_1(t)\ge u_0(t)\) for each fixed t and \(\frac{1}{2}\le u_{n-1}(t)\le u_{n}(t)\le \frac{1}{1-a} \quad t \ge Y\) for all \(n\ge 1\). Thus, \((u_n)_{n\in \mathbb {N}}\) converges pointwise to a function u. By Lebesgue’s Dominated Convergence Theorem, u is a fixed point of \(\Phi \) in V, which shows that there is a non-oscillatory solution. This completes the proof of the theorem.\(\square \)
In Theorem 3.2, we use a constant \(\beta \), quotient of two odd positive integers with \(\beta < \alpha \), for which
Existence of such constant can be established by taking \(g_j(t)=|y|^\delta {\text {sgn}}(t)\), with \(\beta >\delta \). The assumption upon \(\beta \) can be withdrawn by taking \(|u|^\beta {\text {sgn}}(u)\) instead of \(u^\beta \).
Theorem 3.2
Let (a), (c)–(g) and (3.6) hold for \(t \ge t_0\). Then, every solution of (1.1) is oscillatory if
Proof
Let u(t) be an eventually positive solution of (1.1). Then, proceeding as in Theorem , we have \(t_2>t_1>t_0\), such that Eq. (3.4) holds for all \(t \ge t_2\). Using (e), there exists \(t_3>t_2\) for which \(P(t)-P(t_3)\ge \frac{1}{2} P(t)\) for \(t \ge t_3\). Integrating (3.4) from \(t_3\) to t, we have
that is
Since \(p(t)\big (w'(t)\big )^\alpha \) is non-increasing and positive, then there exists \(c>0\) and \(t_4>t_3\), such that \(p(t)\big (w'(t)\big )^\alpha \le c^\alpha \) for \(t \ge t_4\). Integrating the relation \(w'(t) \le cp^{-1/\alpha }(t)\) from \(t_4\) to t, we have
that is
Using (3.6) and (3.9), we obtain
Using (3.10) in (3.8), we obtain
Hence
where
Now
which shows that U(t) is non-increasing on \([t_4,\infty )\) and \(\lim _{t\rightarrow \infty }U(t)\) exists. Using (3.11) and (a), we find
Now, integrating (3.13) from \(t_4\) to t, we have
that is
which contradicts (3.7). This completes the proof. \(\square \)
Example 3.1
Consider the neutral differential equation
Here, \(\alpha = 1/3\), \(p(t)=1\), \(0<q(t)=\mathrm {e}^{-t}<1\) \(\nu _j(t)= t-(j+1)\), \(g_j(t)=t^{(4j+3)/3}\). For \(\beta =5/3\), we have \(\delta _j=(4j+3)/3>\beta =5/3>\alpha =1/3\), and \(g_1(t)/t^\beta =t^{2/3}\) and \(g_2(t)/t^\beta =t^{2}\) which are both increasing functions. Now, we check (3.2). We have
Therefore, all the conditions of of Theorem 3.1 hold. Thus, each solution of (3.14) is oscillatory.
Example 3.2
Consider the neutral differential equation
Here, \(\alpha = 11/3\), \(p(t)=\mathrm {e}^{-t}\), \(0<q(t)=\mathrm {e}^{-t}<1\), \(\nu _j(t)= t-(j+1)\), \(P(t)= \int _{0}^t \mathrm {e}^{3s/11} ds=\frac{11}{3}(\mathrm {e}^{3t/11}-1)\), \(g_j(t)=t^{(4j-3)/3}\). For \(\beta =7/3\), we have \(\delta _j=(4j-3)/3<\beta =7/3<\alpha =11/3\), and \(g_1(t)/t^\beta =t^{-2}\) and \(g_2(t)/t^\beta =t^{-2/3}\) which are both decreasing functions. Now, we check (3.7). We have
Therefore, all the conditions of Theorem 3.2 hold, and therefore, each solution of (3.15) is oscillatory.
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References
Berezansky, L., Domoshnitsky, A., Koplatadze, R.: Oscillation, Nonoscillation, Stability and Asymptotic Properties for Second and Higher Order Functional Differential Equations. CRC Pres, Boca Raton (2020)
Agarwal, R.P., O’Regan, D., Saker, S.H.: Oscillation and Stability of Delay Models in Biology. Springer, New York (2014)
Baculíková, B., Li, T., Džurina, J.: Oscillation theorems for second order neutral differential equations. Electron. J. Qual. Theory Differ. Equ. 74, 1–13 (2011)
Arul, R., Shobha, V.S.: Oscillation of second order neutral differential equations with mixed neutral term. Int. J. Pure Appl. Math. 104(2), 181–191 (2015)
Thandapani, E., Rama, R.: Oscillation criteria for second-order nonlinear neutral differential equations of mixed type. Electron. J. Qual. Theory Differ. Equ. 75, 1–16 (2012)
Thandapani, E., Selvarangam, S., Vijaya, M., Rama, R.: Oscillation results for second order nonlinear differential equation with delay and advanced arguments. Kyungpook Math. J. 56, 137–146 (2016)
Thandapani, E., Padmavathi, S., Pinelas, S.: Oscillation criteria for even-order nonlinear neutral differential equations of mixed type. Bull. Math. Anal. Appl. 6(1), 9–22 (2014)
Li, T., Thandapani, E.: Oscillation of solutions to odd-order nonlinear neutral functional differential equations. Electron. J. Differ. Equ. 2011(23), 1–12 (2011)
Thandapani, E., Padmavathy, S., Pinelas, S.: Oscillation criteria for odd-order nonlinear differential equations with advanced and delayed arguments. Electron. J. Differ. Equ. 2014(174), 1–13 (2014)
Pinelas, S., Santra, S.S.: Necessary and sufficient condition for oscillation of nonlinear neutral first-order differential equations with several delays. J. Fixed Point Theory Appl. 20, Article number: 27 (2018)
Santra, S.S., Ghosh, T., Bazighifan, O.: Explicit criteria for the oscillation of second-order differential equations with several sub-linear neutral coefficients. Adv. Differ. Equ. 2020, 643 (2020)
Santra, S.S., Dassios, I., Ghosh, T.: On the asymptotic behavior of a class of second-order non-linear neutral differential equations with multiple delays. Axioms 9, 134 (2020)
Santra, S.S.: Necessary and sufficient conditions for oscillation of second-order delay differential equations. Tatra Mt. Math. Publ. 75, 135–146 (2020)
Öcalan, O., Kili, N., Özkan, U.: Oscillatory behavior of nonlinear advanced differential equations with a non-monotone argument. Acta Math. Univ. Comenianae 88(2), 239–246 (2019)
Li, T., Rogovchenko, Y.V.: Oscillation theorems for second-order nonlinear neutral delay differential equations. Abstr. Appl. Anal. 2014(ID 594190), 1–11 (2014)
Li, T., Rogovchenko, Y.V.: Oscillation of second-order neutral differential equations. Math. Nachr. 288, 1150–1162 (2015)
Li, Q., Wang, R., Chen, F., Li, T.: Oscillation of second-order nonlinear delay differential equations with nonpositive neutral coefficients. Adv. Differ. Equ. 20, 7 (2015)
Li, T., Rogovchenko, Y.V.: Oscillation criteria for second-order superlinear Emden-Fowler neutral differential equations. Monatsh. Math. 184, 489–500 (2017)
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Santra, S.S., Scapellato, A. Some conditions for the oscillation of second-order differential equations with several mixed delays. J. Fixed Point Theory Appl. 24, 18 (2022). https://doi.org/10.1007/s11784-021-00925-6
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DOI: https://doi.org/10.1007/s11784-021-00925-6