Size distribution of particles in Saturn's rings from aggregation and fragmentation

Saturn's rings consist of a huge number of water ice particles, with a tiny addition of rocky material. They form a flat disk, as the result of an interplay of angular momentum conservation and the steady loss of energy in dissipative inter-particle collisions. For particles in the size range from a few centimeters to a few meters, a power-law distribution of radii, $\sim r^{-q}$ with $q \approx 3$, has been inferred; for larger sizes, the distribution has a steep cutoff. It has been suggested that this size distribution may arise from a balance between aggregation and fragmentation of ring particles, yet neither the power-law dependence nor the upper size cutoff have been established on theoretical grounds. Here we propose a model for the particle size distribution that quantitatively explains the observations. In accordance with data, our model predicts the exponent $q$ to be constrained to the interval $2.75 \le q \le 3.5$. Also an exponential cutoff for larger particle sizes establishes naturally with the cutoff-radius being set by the relative frequency of aggregating and disruptive collisions. This cutoff is much smaller than the typical scale of micro-structures seen in Saturn's rings

Estimation of number of runaway electrons per avalanche in Earth's atmosphere

The connection between thunderstorms and relativistic runaway electron avalanches is an important topic that has attracted the attention of many researchers. Among other things, there are a lot of various simulations of the dynamics of electron avalanches. This article was written mostly in response to the article "The critical avalanche of runaway electrons" by Evgeny Oreshkin et al, which shows rather large numbers for an estimate of the number of runaway electrons, but it also contains the results of our own simulation and comparison with other papers

EXPERIMENTAL TESTS OF CONCRETE MEANS OF PROTECTION FOR COAL MINES DISTRICT ROADWAYS

The current paper is devoted to experimental tests of working protection means in the construction of which concrete in liquid state is used. Such means of protection are most vulnerable to irreversible deformations during the period of their hardening, which coincides with the period of intensive growth of pressure on them from the side of the rock massif. Studies have shown that the pressure of fake rocks on the working protection means depends significantly on the depth of its location and the category of collapse of the roof of the coal seam. The maximum pressure is reached at the moment before the collapse of the roof, that is, at the maximum values of the length of the console of fake rocks, which hangs over the produced longwall space and rests on the working protection means. It was established that the pressure of the fake roof of the coal seam and the relative vertical deformation of the district roadway protection means increase according to the logarithmic dependence of the distance to the longwall outcrop and the time of concrete hardening. With heavy and medium roof collapse, these processes are divided into two stages: in the first stage (the length of which corresponds to the step of the roof collapse), as the longwall moves, the pressure increases intensively, at the moment of collapse it drops by 15-20%, and in the second stage again increases, but 6-8 times more slowly than in the first one, and, provided the relative vertical deformation of the protective device stabilises, passes into a stable mode. With an easily collapsed roof, the step of its collapse does not have a significant effect on the growth and stabilisation of the stress-deformed state of the protective device. The mechanism was revealed and the regularities of loading and deformation of district roadway protection means from a quick-setting mixture depending on the time of its hardening and the distance to the outcrop of longwall, taking into account the category of stability of the roof of the coal seam, were established. Implementation of recommendations for the parameters and technology of the construction of a guard-isolation wall in the conditions of the "Chervonogradska" and "Lisova" mines of the SE "Lvivvugilya" made it possible to reduce the costs of cement-mineral mixture by 27% and save the belt roadways No. 562 and No. 166 for reuse in the production as ventilation during the working out of the adjacent trench column

Безперервна професійна освіта – пріоритетний напрям підвищення фахової компетентності лікарів: досвід, досягнення, проблеми та перспективи розвитку

Continuing education in terms of improving the professional competence of doctors has a great importance. In May 2020 for the first time in Ukraine under conditions of quarantine connected with COVID-19 the Prydniprovsk Association of Internal Medicine Doctors organized a 2-day international conference on internal medicine in a web format. The purpose of the work was to organize, conduct, determine the effectiveness of the international conference of internists in online format and analyze the results of the survey of students. A questionnaire which included 28 test tasks was developed to obtain a feedback from the lecturers. The answers were analyzed and the reasons for possible errors were considered. The level of knowledge acquired by students is generally quite high; however, the most problematic issues were the most modern diagnostic methods in gastroenterology, ECG diagnostics, clinical pharmacology in cardiology and pulmonology. The prospect of developing a system of continuing professional education for internists is to improve teaching methods with the subsequent involvement of leading specialists in various therapeutic areas to cover current issues of medical science and practice.Непрерывное профессиональное образование – приоритетное направление повышения профессиональной компетентности врачей: опыт, достижения, проблемы и перспективы развития. Перцева Т.А., Курята А.В., Конопкина Л.И., Белослудцева К.О., Стадничук Г.М. Непрерывное образование в разрезе повышения профессиональной компетентности врачей приобретает немалое значение. В мае 2020 года впервые в Украине в условиях карантина в связи с COVID-19 Общественной организацией «При­днепровская ассоциация врачей-интернистов» было организовано проведение в веб-формате 2-дневной международной конференции по вопросам внутренней медицины. Целью работы было организовать, провести, определить эффективность проведения международной конференции врачей-интернистов в онлайн-формате и проанализировать результаты опроса слушателей. Для получения обратной связи лекторами была разработана анкета, в которую вошли 28 тестовых заданий. Ответы были про­анализированы, рассмотрены причины возможных ошибок. Уровень усвоенных слушателями новых знаний в целом достаточно высок; впрочем, наиболее проблемными оказались вопросы современных методов диагностики в гастроэнтерологии, ЭКГ-диагностики, клинической фармакологии в кардиологии и пуль­монологии. Перспективой развития системы непрерывного профессионального образования для врачей-интернистов является усовершенствование методов обучения с последующим привлечением ведущих специалистов по различным терапевтическим направлениям к освещению актуальных вопросов медицинской науки и практики

La mise en place de la gratuité des soins dans les pays les plus pauvres : une décision politique

Le Ghana, le Népal, le Soudan viennent de franchir le pas : ils ont choisi la gratuité des soins de santé primaire, soit pour tous, soit pour une partie de leur population. Ils ne sont pas les premiers à s’engager dans cette voie : le nombre des pays en développement qui remettent en cause le système de paiement direct des soins par les usagers, promu par l’Initiative de Bamako depuis 1987, ne cesse d’augmenter. Le fait est que cette stratégie n’a pas tenu ses promesses : instaurée dans le but de proposer des alternatives au financement de la santé des pays pauvres par les États, et d’associer les populations aux évolutions de leur propre système de santé publique, sa contribution à l’amélioration de la qualité des soins est contestable, d’autant que sa composante pour garantir l’accès aux soins des indigents n’a pas été mise en place. Aujourd’hui comme hier, les dépenses de santé font basculer des millions de familles dans la pauvreté et excluent les pauvres de l’accès aux soins

La mise en place de la gratuité des soins dans les pays les plus pauvres : une décision politique

Le Ghana, le Népal, le Soudan viennent de franchir le pas : ils ont choisi la gratuité des soins de santé primaire, soit pour tous, soit pour une partie de leur population. Ils ne sont pas les premiers à s’engager dans cette voie : le nombre des pays en développement qui remettent en cause le système de paiement direct des soins par les usagers, promu par l’Initiative de Bamako depuis 1987, ne cesse d’augmenter. Le fait est que cette stratégie n’a pas tenu ses promesses : instaurée dans le but de proposer des alternatives au financement de la santé des pays pauvres par les États, et d’associer les populations aux évolutions de leur propre système de santé publique, sa contribution à l’amélioration de la qualité des soins est contestable, d’autant que sa composante pour garantir l’accès aux soins des indigents n’a pas été mise en place. Aujourd’hui comme hier, les dépenses de santé font basculer des millions de familles dans la pauvreté et excluent les pauvres de l’accès aux soins