<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Publishing DTD v1.3 20210610//EN" "JATS-journalpublishing1-3.dtd">
<article article-type="research-article" dtd-version="1.3" 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" xml:lang="ru"><front><journal-meta><journal-id journal-id-type="publisher-id">izmertech</journal-id><journal-title-group><journal-title xml:lang="ru">Измерительная техника</journal-title><trans-title-group xml:lang="en"><trans-title>Izmeritel`naya Tekhnika</trans-title></trans-title-group></journal-title-group><issn pub-type="ppub">0368-1025</issn><issn pub-type="epub">2949-5237</issn><publisher><publisher-name>ФГУП "ВНИИФТРИ"</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.32446/0368-1025it.2025-1-43-49</article-id><article-id custom-type="elpub" pub-id-type="custom">izmertech-2268</article-id><article-categories><subj-group subj-group-type="heading"><subject>Research Article</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="ru"><subject>К 70-ЛЕТИЮ ВНИИФТРИ</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="en"><subject>ON THE 70TH ANNIVERSARY OF VNIIFTRI</subject></subj-group></article-categories><title-group><article-title>Меры счётной концентрации частиц в жидкости для обеспечения метрологической прослеживаемости в области сверхвысоких концентраций.</article-title><trans-title-group xml:lang="en"><trans-title>Measures of the number concentration of particles in liquids for the purpose of metrological traceability in the field of ultrahigh concentrations</trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0002-8653-3267</contrib-id><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Аверкин</surname><given-names>Д. В.</given-names></name><name name-style="western" xml:lang="en"><surname>Averkin</surname><given-names>D. V.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Дмитрий Вадимович Аверкин</p></bio><bio xml:lang="en"><p>Dmitry V. Averkin</p></bio><email xlink:type="simple">averkindmitry@gmail.com</email><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Добровольский</surname><given-names>В. И.</given-names></name><name name-style="western" xml:lang="en"><surname>Dobrovolskiy</surname><given-names>V. I.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Владимир Иванович Добровольский</p></bio><bio xml:lang="en"><p>Vladimir I. Dobrovolskiy</p></bio><email xlink:type="simple">vid@vniiftri.ru</email><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Балаханов</surname><given-names>Д. М.</given-names></name><name name-style="western" xml:lang="en"><surname>Balakhanov</surname><given-names>D. M.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Дмитрий Михайлович Балаханов</p></bio><bio xml:lang="en"><p>Dmitry M. Balakhanov</p></bio><email xlink:type="simple">balakhanov@vniiftri.ru</email><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Аверкина</surname><given-names>М. А.</given-names></name><name name-style="western" xml:lang="en"><surname>Averkina</surname><given-names>M. A.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Мария Алексеевна Аверкина</p></bio><bio xml:lang="en"><p>Maria A. Averkina</p></bio><email xlink:type="simple">averkina@vniiftri.ru</email><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0003-4228-8607</contrib-id><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Балаханов</surname><given-names>М. В.</given-names></name><name name-style="western" xml:lang="en"><surname>Balakhanov</surname><given-names>M V.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Михаил Валентинович Балаханов</p></bio><bio xml:lang="en"><p>Mikhail V. Balakhanov</p></bio><email xlink:type="simple">balah@vniiftri.ru</email><xref ref-type="aff" rid="aff-1"/></contrib></contrib-group><aff-alternatives id="aff-1"><aff xml:lang="ru"><institution>Всероссийский научно-исследовательский институт физико-технических и радиотехнических измерений</institution><country>Россия</country></aff><aff xml:lang="en"><institution>Russian Metrological Institute of Technical Physics and Radio Engineering</institution><country>Russian Federation</country></aff></aff-alternatives><pub-date pub-type="collection"><year>2025</year></pub-date><pub-date pub-type="epub"><day>03</day><month>04</month><year>2025</year></pub-date><volume>74</volume><issue>1</issue><fpage>43</fpage><lpage>49</lpage><permissions><copyright-statement>Copyright &amp;#x00A9; ФГУП "ВНИИФТРИ", 2025</copyright-statement><copyright-year>2025</copyright-year><copyright-holder xml:lang="ru">ФГУП "ВНИИФТРИ"</copyright-holder><copyright-holder xml:lang="en">ФГУП "ВНИИФТРИ"</copyright-holder><license xlink:href="https://www.izmt.ru/jour/about/submissions#copyrightNotice" xlink:type="simple"><license-p>https://www.izmt.ru/jour/about/submissions#copyrightNotice</license-p></license></permissions><self-uri xlink:href="https://www.izmt.ru/jour/article/view/2268">https://www.izmt.ru/jour/article/view/2268</self-uri><abstract><p>Измерения гранулометрического состава аэрозолей, суспензий и порошкообразных материалов в области сверхвысоких концентраций востребованы в химической, газовой, нефтяной отраслях промышленности, где используются концентрированные суспензии твёрдых частиц. Существующие средства измерений счётной концентрации частиц в жидкости характеризуются верхней границей диапазона воспроизведения счётной концентрации частиц 1012 м–3, однако для метрологического обеспечения фотометрических высокоточных средств измерений счётной концентрации частиц в жидкости требуется расширить данный диапазон до 10 8 –1018 м–3 . В рамках разработки мер счётной концентрации частиц в жидкости МСК-В предложена технология получения высококонцентрированных суспензий монодисперсных полистирольных латексных сфер. Высокая концентрация суспензии достигнута в результате увеличения количества стирола в затравочной эмульсии и, следовательно, увеличения количества коагулята в процессе синтеза. Описан алгоритм косвенных измерений счётной концентрации частиц в водных суспензиях монодисперсных полистирольных латексных сфер. При исследованиях применено оборудование из состава Государственного первичного эталона единиц дисперсных параметров аэрозолей, взвесей и порошкообразных материалов ГЭТ 163-2020. Определены счётные концентрации частиц и метрологические характеристики созданных мер. Рассчитаны доверительные границы погрешности косвенного измерения счётной концентрации частиц в воде и установлено, что границы относительной погрешности составляют ±4 %. Разработанные меры счётной концентрации частиц в жидкости МСК-В частично закроют потребность внутреннего рынка в мерах и стандартных образцах для определения размера и счётной концентрации частиц при обеспечении единства измерений гранулометрического состава аэрозолей, суспензий и порошкообразных материалов.</p></abstract><trans-abstract xml:lang="en"><p>Measurements of the granulometric composition of aerosols, suspensions and powdery materials in the field of ultrahigh concentrations are in demand in the chemical, gas, and oil industries, where concentrated suspensions of solid particles are used. The existing measuring instruments for particle number concentration in liquids are characterized by an upper limit of the reproduction range of particle number concentration of 1012 m−3. However, for metrological support of photometric high-precision measuring instruments for the number concentration of particles in a liquid, it is necessary to expand this range to 108‒1018 m−3. As part of the development of measures for calculating the concentration of particles in the liquid MSK-V, a technology for producing highly concentrated suspensions of monodisperse polystyrene latex spheres has been proposed. The high concentration of the suspension was achieved as a result of an increase in the amount of styrene in the seeded emulsion and, consequently, an increase in the amount of coagulate during synthesis. An algorithm for indirect measurements of the particle number concentration in aqueous suspensions of monodisperse polystyrene latex spheres is described. During the research, equipment from the State primary standard of units of dispersed parameters of aerosols, suspensions and powdery materials GET 163-2020 was used. The particle number concentrations and metrological characteristics of the created measures are determined. The levels of confidence of the error of indirect measurement of the number concentration of particles in water are calculated. It is established that the limits of the relative error of indirect measurements of the number concentration of particles in water are ±4 %. The developed measures of number concentrations of particles in a liquid (MSK-V) will partially cover the need of the domestic market for measures and standard samples for determining the size and number concentration of particles while ensuring the uniformity of measurements of the granulometric composition of aerosols, suspensions, and powdery materials.</p></trans-abstract><kwd-group xml:lang="ru"><kwd>частица</kwd><kwd>полистирольные латексы</kwd><kwd>микроэмульсия</kwd><kwd>суспензия</kwd><kwd>государственный первичный эталон</kwd><kwd>дисперсные параметры</kwd><kwd>аэрозоль</kwd><kwd>взвесь</kwd><kwd>порошкообразные материалы</kwd><kwd>мера</kwd><kwd>эмульсионная полимеризация</kwd><kwd>коллоидная частица</kwd></kwd-group><kwd-group xml:lang="en"><kwd>particle</kwd><kwd>polystyrene latexes</kwd><kwd>microemulsion</kwd><kwd>suspension</kwd><kwd>national primary standard</kwd><kwd>emulsion polymerization</kwd><kwd>colloidal particle</kwd></kwd-group><funding-group><funding-statement xml:lang="ru">Работа выполнена в рамках договора от 19.06.2023 № 1687/23, являющегося составной частью государственного контракта от 17.05.2023 № 120-38/2023 на выполнение опытно-конструкторской работы по теме «Разработка и выпуск новых комплексов стандартных образцов и мер для обеспечения единства измерений по приоритетным направлениям в целях технологического суверенитета Российской Федерации» (шифр ОКР «Суверенитет»).</funding-statement></funding-group></article-meta></front><back><ref-list><title>References</title><ref id="cit1"><label>1</label><citation-alternatives><mixed-citation xml:lang="ru">Балаханов М. В., Добровольский В. И., Балаханов Д. М., Беленький Д. И., Магомедов Т. М. Состояние метро логического обеспечения измерений дисперсных параметров аэрозолей, взвесей и порошкообразных материалов. Материалы III Международной научно-технической конференции «Метрология физико-химических измерений», 09–11 октября 2018 г., Менделеево, ФГУП «ВНИИФТРИ», с. 108–112 (2019). https://www.elibrary.ru/hgtfcc</mixed-citation><mixed-citation xml:lang="en">Balakhanov M. V., Dobrovolsky V. I., Balakhanov D. M., Belenky D. I., Magomedov T. M. The state of metrological support for measurements of dispersed parameters of aerosols, suspensions and powdery materials. Materials of the III International Scientific and Technical Conference “Metrology of physico-chemical measurements”, October 09–11, 2018, Mendeleevo, VNIIFTRI, pp. 108–112 (2019). (In Russ.) https://www.elibrary.ru/hgtfcc</mixed-citation></citation-alternatives></ref><ref id="cit2"><label>2</label><citation-alternatives><mixed-citation xml:lang="ru">Садагов А. Ю. Диагностика коллоидных систем на основе совместного использования спектров абсорбции, флуоресценции, статического и динамического рассеяния света: автореф. дис. канд. техн. наук. ВНИИОФИ, Москва (2018). https://www.vniiofi.ru/images/DISS_SOVET/avtoreferat/Dissertatciia_Sadagov.pdf</mixed-citation><mixed-citation xml:lang="en">Sedakov A. Y. Diagnostics of colloidal systems based on the joint use of absorption, fluorescence, static and dynamic light scattering spectra: Avtoref. candidate’s dissertation Technical Sciences, VNIIOFI, Moskow (2018). (In Russ.) https://www.vniiofi.ru/images/DISS_SOVET/avtoreferat/Dissertatciia_Sadagov.pdf</mixed-citation></citation-alternatives></ref><ref id="cit3"><label>3</label><citation-alternatives><mixed-citation xml:lang="ru">Грицкова И. А., Жаченков С. В., Прокопов Н. И., Ильменев П. Е. Эмульсионная полимеризация гидрофобных мономеров в высокодисперсных эмульсиях. Высокомолекулярные соединения. Серия А, 33(7), 1476–1483 (1991). https://www.elibrary.ru/xpoauo</mixed-citation><mixed-citation xml:lang="en">Gritskova I. A., Zhachenkov S. V., Prokopov N. I., Ilmenev P. E. Emulsion polymerization of hydrophobic monomers in high-dispersed emulsions. Vysokomolekulyarnye soedineniya. Seriya A, 33(7), 1476–1483 (1991). (In Russ.). https://www.elibrary.ru/xpoauo</mixed-citation></citation-alternatives></ref><ref id="cit4"><label>4</label><citation-alternatives><mixed-citation xml:lang="ru">Прокопов Н. И., Грицкова И. А. Особенности гетерофазной полимеризации стирола при образовании поверхностно-активных веществ на границе раздела фаз. Успехи химии, (9), 890–900 (2001). https://doi.org/10.1070/rc2001v070n09abeh000669</mixed-citation><mixed-citation xml:lang="en">Prokopov N. I., Gritskova I. A. Characteristic features of heterophase polymerisation of styrene with simultaneous formation of surfactants at the interface. Russian Chemical Reviews, 9, 890–900 (2001). https://doi.org/10.1070/rc2001v070n09abeh000669</mixed-citation></citation-alternatives></ref><ref id="cit5"><label>5</label><citation-alternatives><mixed-citation xml:lang="ru">Аверкин Д. В., Кузнецов И. А., Балаханов Д. М. Разработка мер размеров частиц в жидкости с номинальным значением размеров частиц 0,07 мкм и 0,1 мкм. Альманах современной метрологии, (4(36)), 87–95 (2023). https://elibrary.ru/brezme</mixed-citation><mixed-citation xml:lang="en">Averkin D. V., Kuznetsov I. A., Balakhanov D. M. Development of particle size measures in a liquid with a nominal particle size value of 0.07 microns and 0.1 microns. Al'manac of Modern Metrology, (4(36)), 87–95 (2023). https://elibrary.ru/brezme</mixed-citation></citation-alternatives></ref><ref id="cit6"><label>6</label><citation-alternatives><mixed-citation xml:lang="ru">Brouwer W. M. The preparation of small polystyrene latex particles. Journal of Applied Polymer Science, 38, 1335–1346 (1989). https://doi.org/10.1002/app.1989.070380712</mixed-citation><mixed-citation xml:lang="en">Brouwer W. M. The preparation of small polystyrene latex particles. Journal of Applied Polymer Science, 38, 1335–1346 (1989). https://doi.org/10.1002/app.1989.070380712</mixed-citation></citation-alternatives></ref><ref id="cit7"><label>7</label><citation-alternatives><mixed-citation xml:lang="ru">Ugelstad J.; El-Aasser M. S., Vanderhoff J. W. Emulsion polymerization: Initiation of polymerization in monomer droplets. Polymer Letters Edition, 11, 503–513 (1973). https://doi.org/10.1002/pol.1973.130110803</mixed-citation><mixed-citation xml:lang="en">Ugelstad J.; El-Aasser M. S., Vanderhoff J. W. Emulsion polymerization: Initiation of polymerization in monomer droplets. Polymer Letters Edition, 11, 503–513 (1973). https://doi.org/10.1002/pol.1973.130110803</mixed-citation></citation-alternatives></ref><ref id="cit8"><label>8</label><citation-alternatives><mixed-citation xml:lang="ru">Paulen R., Benyahia B., Latifi M. A., Fikar M. Dynamic optimization of semi-batch emulsion co-polymerization reactor for styrene/butyl acrylate in the presence of a chain transfer agent. Computer Aided Chemical Engineering, 32, 721–726 (2013). https://doi.org/10.1016/B978-0-444-63234-0.50121-4</mixed-citation><mixed-citation xml:lang="en">Paulen R., Benyahia B., Latifi M. A., Fikar M. Dynamic optimization of semi-batch emulsion co-polymerization reactor for styrene/butyl acrylate in the presence of a chain transfer agent. Computer Aided Chemical Engineering, 32, 721–726 (2013). https://doi.org/10.1016/B978-0-444-63234-0.50121-4</mixed-citation></citation-alternatives></ref><ref id="cit9"><label>9</label><citation-alternatives><mixed-citation xml:lang="ru">Macbeth A. J., Lin Zh., Goddard J. M. General method for emulsion polymerization to yield functional terpolymers. MethodsX, 7, 101110 (2020). https://doi.org/10.1016/j.mex.2020.101110</mixed-citation><mixed-citation xml:lang="en">Macbeth A. J., Lin Zh., Goddard J. M. General method for emulsion polymerization to yield functional terpolymers. MethodsX, 7, 101110 (2020). https://doi.org/10.1016/j.mex.2020.101110</mixed-citation></citation-alternatives></ref><ref id="cit10"><label>10</label><citation-alternatives><mixed-citation xml:lang="ru">Wang T., Shi S., Yang F., Zhou L. M., Kuroda S. Poly(methyl methacrylate)/polystyrene composite latex particles with a novel core/shell morphology. Journal of Materials Science, 45, 3392–3395 (2010). https://doi.org/10.1007/s10853-010-4449-9</mixed-citation><mixed-citation xml:lang="en">Wang T., Shi S., Yang F., Zhou L. M., Kuroda S. Poly(methyl methacrylate)/polystyrene composite latex particles with a novel core/shell morphology. Journal of Materials Science, 45, 3392–3395 (2010). https://doi.org/10.1007/s10853-010-4449-9</mixed-citation></citation-alternatives></ref><ref id="cit11"><label>11</label><citation-alternatives><mixed-citation xml:lang="ru">Fan X., Jia X., Zhang H., Zhang B., Li Ch., Zhang Q. Synthesis of Raspberry-Like Poly(styrene–glycidyl methacrylate) Particles via a one-step soap-free emulsion polymerization process accompanied by phase separation. Langmuir, 29, 11730– 11741 (2013). https://doi.org/10.1021/la402759w</mixed-citation><mixed-citation xml:lang="en">Fan X., Jia X., Zhang H., Zhang B., Li Ch., Zhang Q. Synthesis of Raspberry-Like Poly(styrene–glycidyl methacrylate) Particles via a one-step soap-free emulsion polymerization process accompanied by phase separation. Langmuir, 29, 11730– 11741 (2013). https://doi.org/10.1021/la402759w</mixed-citation></citation-alternatives></ref><ref id="cit12"><label>12</label><citation-alternatives><mixed-citation xml:lang="ru">Sudol E. D., El-Aasser M. S., Vanderhoff J. W. Kinetics of successive seeding of monodisperse polystyrene latexes. I. Initiation via potassium persulfate. Journal of Polymer Science, Part A: Polymer Chemistry, 24, 3499–3513 (1986). https://doi.org/10.1002/pola.1986.080241230</mixed-citation><mixed-citation xml:lang="en">Sudol E. D., El-Aasser M. S., Vanderhoff J. W. Kinetics of successive seeding of monodisperse polystyrene latexes. I. Initiation via potassium persulfate. Journal of Polymer Science, Part A: Polymer Chemistry, 24, 3499–3513 (1986). https://doi.org/10.1002/pola.1986.080241230</mixed-citation></citation-alternatives></ref><ref id="cit13"><label>13</label><citation-alternatives><mixed-citation xml:lang="ru">Vanderhoff J. W., Vitkuske J. F., Bradford E. B., Alfrey Jr. T. Some factors involved in the preparation of uniform particle size latexes. Journal of Polymer Science, 20, 225–234 (1956). https://doi.org/10.1002.pol.1956.120209501</mixed-citation><mixed-citation xml:lang="en">Vanderhoff J. W., Vitkuske J. F., Bradford E. B., Alfrey Jr. T. Some factors involved in the preparation of uniform particle size latexes. Journal of Polymer Science, 20, 225–234 (1956). https://doi.org/10.1002.pol.1956.120209501</mixed-citation></citation-alternatives></ref><ref id="cit14"><label>14</label><citation-alternatives><mixed-citation xml:lang="ru">Thomson B., Rudin A., Lajoie G. Dispersion copolymerization of styrene and divinylbenzene: Synthesis of monodisperse, uniformly crosslinked particles. Journal of Polymer Science, Part A: Polymer Chemistry, 33, 345–357 (1995). https://doi.org/10.1002/pola.1995.080330301</mixed-citation><mixed-citation xml:lang="en">Thomson B., Rudin A., Lajoie G. Dispersion copolymerization of styrene and divinylbenzene: Synthesis of monodisperse, uniformly crosslinked particles. Journal of Polymer Science, Part A: Polymer Chemistry, 33, 345–357 (1995). https://doi.org/10.1002/pola.1995.080330301</mixed-citation></citation-alternatives></ref><ref id="cit15"><label>15</label><citation-alternatives><mixed-citation xml:lang="ru">Qi H., Hao W., Xu H. et al. Synthesis of large-sized monodisperse polystyrene microspheres by dispersion polymerization with dropwise monomer feeding procedure. Colloid and Polymer Science, 287, 243–248 (2009). https://doi.org/10.1007/s00396-008-1979-7</mixed-citation><mixed-citation xml:lang="en">Qi H., Hao W., Xu H. et al. Synthesis of large-sized monodisperse polystyrene microspheres by dispersion polymerization with dropwise monomer feeding procedure. Colloid and Polymer Science, 287, 243–248 (2009). https://doi.org/10.1007/s00396-008-1979-7</mixed-citation></citation-alternatives></ref><ref id="cit16"><label>16</label><citation-alternatives><mixed-citation xml:lang="ru">Аверкин Д. В. Синтез мер размера частиц на основе водных суспензий полистирольных латексных сфер. Измерительная техника, (12), 64–68 (2022). https://doi.org/10.32446/0368-1025it.2022-12-64-68</mixed-citation><mixed-citation xml:lang="en">Averkin D. V. Synthesis of particle size standards based on aqueous suspensions of polystyrene latex spheres. Measurement Technique, 65(12), 936–941 (2023). https://doi.org/10.1007/s11018-023-02173-1</mixed-citation></citation-alternatives></ref><ref id="cit17"><label>17</label><citation-alternatives><mixed-citation xml:lang="ru">Аверкин Д. В. Влияние поверхностно-активных веществ на степень полидисперсности суспензий полистирольных латексных сфер. Измерительная техника, 73(3), 55–60 (2024). https://doi.org/10.32446/0368-1025it.2024-3-55-60</mixed-citation><mixed-citation xml:lang="en">Averkin D. V. Effect of surfactants on the degree of polydispersity of suspensions of polystyrene latex spheres. Measurement Technique, 67(3), 240–246 (2024). https://doi.org/10.1007/s11018-024-02339-5</mixed-citation></citation-alternatives></ref><ref id="cit18"><label>18</label><citation-alternatives><mixed-citation xml:lang="ru">Балаханов М. В., Добровольский В. И., Балаханов Д. М., Беленький Д. И. Совершенствование Государственного первичного эталона единиц дисперсных параметров аэрозолей, взвесей и порошкообразных материалов ГЭТ 163-2010. Измерительная техника, (12), 3–7 (2018). https://doi.org/10.32446/0368-1025it.2018-12-3-7</mixed-citation><mixed-citation xml:lang="en">Balakhanov M. V., Dobrovolsky V. I., Balakhanov D. M., Belenky D. I. Improvements in Get 163-2010, the State Primary Standard of the units of disperse parameters of aerosols, suspensions, and power-like materials. Measurement Technique, 61(12), 1135–1140 (2019). https://doi.org/10.1007/s11018-019-01560-x</mixed-citation></citation-alternatives></ref><ref id="cit19"><label>19</label><citation-alternatives><mixed-citation xml:lang="ru"></mixed-citation><mixed-citation xml:lang="en"></mixed-citation></citation-alternatives></ref></ref-list><fn-group><fn fn-type="conflict"><p>The authors declare that there are no conflicts of interest present.</p></fn></fn-group></back></article>
