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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">38695</article-id><article-id pub-id-type="doi">10.22363/2413-3639-2024-70-1-38-52</article-id><article-id pub-id-type="edn">YYQSXD</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">The Riemann problem for the main model cases of the Euler-Poisson equations</article-title><trans-title-group xml:lang="ru"><trans-title>Задача Римана для основных модельных случаев уравнений Эйлера-Пуассона</trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author"><name-alternatives><name xml:lang="en"><surname>Gargyants</surname><given-names>L. V.</given-names></name><name xml:lang="ru"><surname>Гаргянц</surname><given-names>Л. В.</given-names></name></name-alternatives><email>gargyants@bmstu.ru</email><xref ref-type="aff" rid="aff1"/></contrib><contrib contrib-type="author"><name-alternatives><name xml:lang="en"><surname>Rozanova</surname><given-names>O. S.</given-names></name><name xml:lang="ru"><surname>Розанова</surname><given-names>О. С.</given-names></name></name-alternatives><email>rozanova@mech.math.msu.su</email><xref ref-type="aff" rid="aff2"/></contrib><contrib contrib-type="author"><name-alternatives><name xml:lang="en"><surname>Turzynsky</surname><given-names>M. K.</given-names></name><name xml:lang="ru"><surname>Турцынский</surname><given-names>М. К.</given-names></name></name-alternatives><email>M13041@yandex.ru</email><xref ref-type="aff" rid="aff3"/><xref ref-type="aff" rid="aff4"/></contrib></contrib-group><aff-alternatives id="aff1"><aff><institution xml:lang="en">Bauman Moscow State Technical University</institution></aff><aff><institution xml:lang="ru">Московский государственный технический университет им. Н.Э. Баумана</institution></aff></aff-alternatives><aff-alternatives id="aff2"><aff><institution xml:lang="en">Lomonosov Moscow State University</institution></aff><aff><institution xml:lang="ru">Московский государственный университет им. М.В. Ломоносова</institution></aff></aff-alternatives><aff-alternatives id="aff3"><aff><institution xml:lang="en">Russian University of Transport</institution></aff><aff><institution xml:lang="ru">Российский университет транспорта (МИИТ)</institution></aff></aff-alternatives><aff-alternatives id="aff4"><aff><institution xml:lang="en">National Research University “Higher School of Economics” (HSE University)</institution></aff><aff><institution xml:lang="ru">Национальный исследовательский университет «Высшая школа экономики»</institution></aff></aff-alternatives><pub-date date-type="pub" iso-8601-date="2024-03-15" publication-format="electronic"><day>15</day><month>03</month><year>2024</year></pub-date><volume>70</volume><issue>1</issue><issue-title xml:lang="en">Functional spaces. Differential operators. Problems of mathematics education</issue-title><issue-title xml:lang="ru">Функциональные пространства. Дифференциальные операторы. Проблемы математического образования</issue-title><fpage>38</fpage><lpage>52</lpage><history><date date-type="received" iso-8601-date="2024-04-09"><day>09</day><month>04</month><year>2024</year></date></history><permissions><copyright-statement xml:lang="en">Copyright ©; 2024, Gargyants L.V., Rozanova O.S., Turzynsky M.K.</copyright-statement><copyright-statement xml:lang="ru">Copyright ©; 2024, Гаргянц Л.В., Розанова О.С., Турцынский М.К.</copyright-statement><copyright-year>2024</copyright-year><copyright-holder xml:lang="en">Gargyants L.V., Rozanova O.S., Turzynsky M.K.</copyright-holder><copyright-holder xml:lang="ru">Гаргянц Л.В., Розанова О.С., Турцынский М.К.</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/38695">https://journals.rudn.ru/CMFD/article/view/38695</self-uri><abstract xml:lang="en"><p>In this paper, we construct a solution to the Riemann problem for an inhomogeneous nonstrictly hyperbolic system of two equations, which is a corollary of the Euler-Poisson equations without pressure [9]. These equations can be considered for the cases of attractive and repulsive forces as well as for the cases of zero and nonzero underlying density background. The solution to the Riemann problem for each case is nonstandard and contains a delta-shaped singularity in the density component. In [16], solutions were constructed for the combination corresponding to the cold plasma model (repulsive force and nonzero background density). In this paper, we consider the three remaining cases.</p></abstract><trans-abstract xml:lang="ru"><p>В статье построено решение задачи Римана для неоднородной нестрого гиперболической системы двух уравнений, являющейся следствием уравнений Эйлера-Пуассона без давления [9]. Эти уравнения могут быть рассмотрены для случаев притягивающей и отталкивающей силы, и для случаев нулевого и ненулевого основного фона плотности. Решение задачи Римана для каждого случая является нестандартным и содержит дельтаобразную сингулярность в компоненте плотности. В [16] построено решение для комбинации, соответствующей модели холодной плазмы (отталкивающая сила и ненулевой фон плотности). В настоящей работе рассмотрены три оставшихся случая.</p></trans-abstract><kwd-group xml:lang="en"><kwd>Euler-Poisson equations</kwd><kwd>Riemann problem</kwd><kwd>characteristics</kwd><kwd>shock wave</kwd><kwd>rarefaction wave</kwd></kwd-group><kwd-group xml:lang="ru"><kwd>уравнения Эйлера-Пуассона</kwd><kwd>задача Римана</kwd><kwd>характеристики</kwd><kwd>ударная волна</kwd><kwd>волна разрежения</kwd></kwd-group><funding-group><funding-statement xml:lang="en">Supported by the Russian Science Foundation grant № 23-1100056 through the Peoples’ Friendship University of Russia named after Patrice Lumumba.</funding-statement><funding-statement xml:lang="ru">Поддержано грантом РНФ № 23-11-00056 через Российский университет дружбы народов.</funding-statement></funding-group></article-meta></front><body></body><back><ref-list><ref id="B1"><label>1.</label><mixed-citation>Гуревич А.В., Зыбин К.П. 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