Branching of negative streamers in free flight

We recently have shown that a negative streamer in a sufficiently high homogeneous field can branch spontaneously due to a Laplacian instability, rather than approach a stationary mode of propagation with fixed radius. In our previous simulations, the streamer started from a wide initial ionization seed on the cathode. We here demonstrate in improved simulations that a streamer emerging from a single electron branches in the same way. In fact, though the evolving streamer is much more narrow, it branches after an even shorter propagation distance.Comment: 4 pages, 3 figure

Stability of negative ionization fronts: regularization by electric screening?

We recently have proposed that a reduced interfacial model for streamer propagation is able to explain spontaneous branching. Such models require regularization. In the present paper we investigate how transversal Fourier modes of a planar ionization front are regularized by the electric screening length. For a fixed value of the electric field ahead of the front we calculate the dispersion relation numerically. These results guide the derivation of analytical asymptotes for arbitrary fields: for small wave-vector k, the growth rate s(k) grows linearly with k, for large k, it saturates at some positive plateau value. We give a physical interpretation of these results.Comment: 11 pages, 2 figure

DETERMINATION OF EXPEDIENCY REPLACEMENT OF ROUTERS IN ІР - NETWORKS ON EQUIPMENT MPLS IN DEPENDENCE ON PARAMETERS OF LOADING

Розглядається перехід від IP-мережі до MPLS без змін кабельної інфраструктури. В якості критерію доцільності заміни маршрутизаторів в ІР-мережі на обладнання MPLS розглядається час затримки передачі пакетів. Виведені аналітичні залежності демонструють, що технологія MPLS в порівнянні з IP має низку переваг, які зростають з рівнем завантаженості мережі. Математичний апарат, наведений в статті, дозволяє провести границю демаркації по критерію часу доставки пакетів між транспортними мережами.В статье рассматривается переход от IP-сетей к MPLS без изменения кабельной инфраструктуры. В качестве критерия целесообразности замены маршрутизаторов в IP-сети на оборудование MPLS рассматривается время задержки передачи пакетов. Выведенные аналитические зависимости демонстрируют, что технология MPLS в сравнении с IP имеет ряд преимуществ, которые возрастают с уровнем загруженности сети. Математический аппарат, приведенный в статье, позволяет провести границу демаркации по критерию времени доставки пакетов между транспортными сетями.In the article a transition is examined from IP-networks to MPLS without the change of cable infrastructure. As a criterion of expediency of replacement of routers in IP-network on the equipment MPLS time of delay transmission of packages is examined. The shown out analytical dependences demonstrate, that technology MPLS by comparison to IP has a row of advantages that increase with the level work-load of network. The mathematical vehicle presented in the article allows to conduct the border of demarcation on the criterion of time of delivery of packages between transport networks

Relativistic electron beams above thunderclouds

International audienceNon-luminous relativistic electron beams above thunderclouds have been detected by the radio signals of low frequency ∼40-400 kHz which they radiate. The electron beams occur ∼2-9 ms after positive cloud-to-ground lightning discharges at heights between ∼22-72 km above thunderclouds. Intense positive lightning discharges can also cause sprites which occur either above or prior to the electron beam. One electron beam was detected without any luminous sprite which suggests that electron beams may also occur independently of sprites. Numerical simulations show that beams of electrons partially discharge the lightning electric field above thunderclouds and thereby gain a mean energy of ∼7 MeV to transport a total charge of ∼−10 mC upwards. The impulsive current ∼3 × 10−3 Am−2 associated with relativistic electron beams above thunderclouds is directed downwards and needs to be considered as a novel element of the global atmospheric electric circuit

Лілія Георгіївна Бойцун (пам'яті математика і яскравої особистості)

The article is devoted to the talented mathematician, candidate of physical and mathematical sciences Boitsun Lilia Georgiivna. The article describes her life and career, scientific activity.Cтаттю присвячено талановитому математику, кандидату фізико-математичних наук Бойцун Лілії Георгіївні. У статті висвітлено її життєвий шлях і трудовий та науковий доробок

Relativistic electron beams above thunderclouds

Non-luminous relativistic electron beams above thunderclouds have been detected by the radio signals of low frequency ~ 40–400 kHz which they radiate. The electron beams occur ~ 2–9 ms after positive cloud-to-ground lightning discharges at heights between ~22–72 km above thunderclouds. Intense positive lightning discharges can also cause sprites which occur either above or prior to the electron beam. One electron beam was detected without any luminous sprite which suggests that electron beams may also occur independently of sprites. Numerical simulations show that beams of electrons partially discharge the lightning electric field above thunderclouds and thereby gain a mean energy of ~ 7MeV to transport a total charge of ~ −10mC upwards. The impulsive current ~3×10−3 Am−2 associated with relativistic electron beams above thunderclouds is directed downwards and needs to be considered as a novel element of the global atmospheric electric circuit.Peer Reviewe