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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">51535</article-id><article-id pub-id-type="doi">10.22363/2413-3639-2026-72-1-85-93</article-id><article-id pub-id-type="edn">TUYAYJ</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">Approximate controllability of a semilinear delayed heat equation Tikhonov regularization</article-title><trans-title-group xml:lang="ru"><trans-title>Приближенная управляемость полулинейного уравнения теплопроводности с запаздыванием с помощью регуляризации Тихонова</trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0002-2736-1848</contrib-id><contrib-id contrib-id-type="scopus">55500517400</contrib-id><contrib-id contrib-id-type="researcherid">C-5056-2017</contrib-id><name-alternatives><name xml:lang="en"><surname>Kumar</surname><given-names>S.</given-names></name><name xml:lang="ru"><surname>Кумар</surname><given-names>С.</given-names></name></name-alternatives><email>suman@igntu.ac.in</email><xref ref-type="aff" rid="aff1"/></contrib></contrib-group><aff id="aff1"><institution>Indira Gandhi National Tribal University</institution></aff><pub-date date-type="pub" iso-8601-date="2026-07-14" publication-format="electronic"><day>14</day><month>07</month><year>2026</year></pub-date><volume>72</volume><issue>1</issue><issue-title xml:lang="en">Differential and Functional Differential Equations</issue-title><issue-title xml:lang="ru">Дифференциальные и функционально-дифференциальные уравнения</issue-title><fpage>85</fpage><lpage>93</lpage><history><date date-type="received" iso-8601-date="2026-07-29"><day>29</day><month>07</month><year>2026</year></date></history><permissions><copyright-statement xml:lang="en">Copyright ©; 2026, Kumar S.</copyright-statement><copyright-statement xml:lang="ru">Copyright ©; 2026, Кумар С.</copyright-statement><copyright-year>2026</copyright-year><copyright-holder xml:lang="en">Kumar S.</copyright-holder><copyright-holder xml:lang="ru">Кумар С.</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/51535">https://journals.rudn.ru/CMFD/article/view/51535</self-uri><abstract xml:lang="en"><p>In this work, we study approximate controllability of a semilinear heat equation with delay using the Tikhonov regularization. The considered problem for partial differential equation is transformed into an equivalent operator equation. We explore sufficient conditions and analyze the operator equation to guarantee the approximate controllability by means of Tikhonov reqularization method. The main result proves that the semilinear delay system is approximately controllable if the corresponding linear nondelay system is approximately controllable. Finally, we establish an error estimate for the Tikhonov regularized solution of an operator equation.</p></abstract><trans-abstract xml:lang="ru"><p>В данной работе исследуется приближенная управляемость полулинейного уравнения теплопроводности с запаздыванием с использованием регуляризации Тихонова. Рассматриваемая задача в виде дифференциального уравнения в частных производных преобразуется в эквивалентное операторное уравнение. Были исследованы достаточные условия и проанализировано операторное уравнение, гарантирующее приближенную управляемость в соответствии с методом регуляризации Тихонова. Основной результат доказывает, что полулинейная система с запаздыванием является приближенно управляемой, если соответствующая линейная система без запаздывания также является приближенно управляемой. В заключение была установлена оценка погрешности для решения операторного уравнения, регуляризованного по Тихонову.</p></trans-abstract><kwd-group xml:lang="en"><kwd>approximate controllability</kwd><kwd>semilinear heat equation</kwd><kwd>delay</kwd><kwd>Tikhonov regularization</kwd><kwd>operator equation</kwd><kwd>ill-posed problem</kwd></kwd-group><kwd-group xml:lang="ru"><kwd>приближенная управляемость</kwd><kwd>полулинейное уравнение теплопроводности</kwd><kwd>запаздывание</kwd><kwd>тихоновская регуляризация</kwd><kwd>операторное уравнение</kwd><kwd>некорректная задача</kwd></kwd-group><funding-group/></article-meta><fn-group/></front><body></body><back><ref-list><ref id="B1"><label>1.</label><mixed-citation>Carrasco A., Leiva H. Approximate controllability of a system of parabolic equations with delay // J. Math. Anal. 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