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<article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" article-type="research-article" dtd-version="1.2" xml:lang="en"><front><journal-meta><journal-id journal-id-type="publisher-id">Contemporary Mathematics. Fundamental Directions</journal-id><journal-title-group><journal-title xml:lang="en">Contemporary Mathematics. Fundamental Directions</journal-title><trans-title-group xml:lang="ru"><trans-title>Современная математика. Фундаментальные направления</trans-title></trans-title-group></journal-title-group><issn publication-format="print">2413-3639</issn><issn publication-format="electronic">2949-0618</issn><publisher><publisher-name xml:lang="en">Peoples’ Friendship University of Russia named after Patrice Lumumba (RUDN University)</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="publisher-id">50760</article-id><article-id pub-id-type="doi">10.22363/2413-3639-2026-72-2-258-281</article-id><article-id pub-id-type="edn">AZYDIE</article-id><article-categories><subj-group subj-group-type="toc-heading" xml:lang="en"><subject>Articles</subject></subj-group><subj-group subj-group-type="toc-heading" xml:lang="ru"><subject>Статьи</subject></subj-group><subj-group subj-group-type="article-type"><subject>Research Article</subject></subj-group></article-categories><title-group><article-title xml:lang="en">Asymptotic behavior of solutions of an incomplete second-order integro-differential equation</article-title><trans-title-group xml:lang="ru"><trans-title>Асимптотическое поведение решений неполного интегро-дифференциального уравнения второго порядка</trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0002-6084-1114</contrib-id><contrib-id contrib-id-type="scopus">25026570600</contrib-id><contrib-id contrib-id-type="spin">4632-1311</contrib-id><name-alternatives><name xml:lang="en"><surname>Zakora</surname><given-names>D. A.</given-names></name><name xml:lang="ru"><surname>Закора</surname><given-names>Д. А.</given-names></name></name-alternatives><email>dmitry.zkr@gmail.com</email><xref ref-type="aff" rid="aff1"/></contrib></contrib-group><aff-alternatives id="aff1"><aff><institution xml:lang="en">V. I. Vernadsky Crimean Federal University</institution></aff><aff><institution xml:lang="ru">Крымский федеральный университет им. В.И. Вернадского</institution></aff></aff-alternatives><pub-date date-type="pub" iso-8601-date="2026-06-16" publication-format="electronic"><day>16</day><month>06</month><year>2026</year></pub-date><volume>72</volume><issue>2</issue><issue-title xml:lang="en"/><issue-title xml:lang="ru"/><fpage>258</fpage><lpage>281</lpage><history><date date-type="received" iso-8601-date="2026-06-22"><day>22</day><month>06</month><year>2026</year></date></history><permissions><copyright-statement xml:lang="en">Copyright ©; 2026, Zakora D.A.</copyright-statement><copyright-statement xml:lang="ru">Copyright ©; 2026, Закора Д.А.</copyright-statement><copyright-year>2026</copyright-year><copyright-holder xml:lang="en">Zakora D.A.</copyright-holder><copyright-holder xml:lang="ru">Закора Д.А.</copyright-holder><ali:free_to_read xmlns:ali="http://www.niso.org/schemas/ali/1.0/"/><license><ali:license_ref xmlns:ali="http://www.niso.org/schemas/ali/1.0/">https://creativecommons.org/licenses/by-nc/4.0</ali:license_ref></license></permissions><self-uri xlink:href="https://journals.rudn.ru/CMFD/article/view/50760">https://journals.rudn.ru/CMFD/article/view/50760</self-uri><abstract xml:lang="en"><p>In this paper, we study an incomplete second-order integro-differential operator equation in a Hilbert space. The difference-type kernel of an integral perturbation is a holomorphic semigroup bordered by unbounded operators. The asymptotic behavior of solutions of this equation is studied. Asymptotic formulas for solutions are proved in the case when the right-hand side is close to an almost periodic function. The obtained formulas are applied to one equation describing a number of applications from the mechanics of viscoelastic systems.</p></abstract><trans-abstract xml:lang="ru"><p>В работе изучается неполное интегро-дифференциальное операторное уравнение второго порядка в гильбертовом пространстве. Ядро разностного типа интегрального возмущения представляет собой голоморфную полугруппу, окаймленную неограниченными операторами. Исследуется асимптотическое поведение решений этого уравнения. Доказаны асимптотические формулы для решений в случае, когда правая часть близка к почти периодической функции. Полученные формулы применены к одному уравнению, описывающему ряд приложений из механики вязкоупругих систем.</p></trans-abstract><kwd-group xml:lang="en"><kwd>operator equation</kwd><kwd>integro-differential equation</kwd><kwd>Cauchy problem</kwd><kwd>solution asymptotics</kwd></kwd-group><kwd-group xml:lang="ru"><kwd>операторное уравнение</kwd><kwd>интегро-дифференциальное уравнение</kwd><kwd>задача Коши</kwd><kwd>асимптотика решения</kwd></kwd-group><funding-group><award-group><funding-source><institution-wrap><institution xml:lang="ru">Работа поддержана Министерством науки и высшего образования Российской Федерации, соглашение № 075-02-2026-1313</institution></institution-wrap><institution-wrap><institution xml:lang="en">The work was supported by the Ministry of Science and Higher Education of the Russian Federation, agreement No. 075-02-2026-1313</institution></institution-wrap></funding-source></award-group></funding-group></article-meta><fn-group/></front><body></body><back><ref-list><ref id="B1"><label>1.</label><mixed-citation>Власов В.В., Раутиан Н.А. 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