High order fluid model for streamer discharges. II. Numerical solution and investigation of planar fronts

The high order fluid model developed in the preceding paper is employed here to study the propagation of negative planar streamer fronts in pure nitrogen. The model consists of the balance equations for electron density, average electron velocity, average electron energy and average electron energy flux. These balance equations have been obtained as velocity moments of Boltzmann's equation and are here coupled to the Poisson equation for the space charge electric field. Here the results of simulations with the high order model, with a PIC/MC (Particle in cell/Monte Carlo) model and with the first order fluid model based on the hydrodynamic drift-diffusion approximation are presented and compared. The comparison with the MC model clearly validates our high order fluid model, thus supporting its correct theoretical derivation and numerical implementation. The results of the first order fluid model with local field approximation, as usually used for streamer discharges, show considerable deviations. Furthermore, we study the inaccuracies of simulation results caused by an inconsistent implementation of transport data into our high order fluid model. We also demonstrate the importance of the energy flux term in the high order model by comparing with results where this term is neglected. Finally, results with an approximation for the high order tensor in the energy flux equation is found to agree well with the PIC/MC results for reduced electric fields up to 1000 Townsend, as considered in this work.Comment: 26 pages, 11 figure

Derivation and test of high order fluid model for streamer discharges

A high order fluid model for streamer dynamics is developed by closing the system after the 4th moment of the Boltzmann equation in local mean energy approximation. This is done by approximating the high order pressure tensor in the heat flux equation through the previous moments. Mathematical characteristics of the system is studied. Then planar ionization fronts for negative streamers in Nsub2 are simulated with the classical streamer model, MC-PIC particle model, and with the present higher order model

Testicular dermoid cyst in a 14-year-old child

ДЕРМОИДНАЯ КИСТА /ДИАГНДЕРМОИД /ДИАГНЯИЧКИ /УЛЬТРАСОНДЕТИКЛИНИЧЕСКИЕ СЛУЧАИВ работе представлен клинический случай ребенка, 14 лет, с дермоидной кистой правого яичка. Образование впервые было выявлено при профилактическом осмотре в поликлинике. В последующем пациенту неоднократно проводилось ультразвуковое исследование наружных половых органов, при котором в верхнем полюсе правого яичка выявлялась неоднородная эхоструктура размерами 14 мм, 13,7 мм и 12 мм с четким, ровным контуром. Результаты иммуноферментного анализа крови не показали увеличение основных маркеров опухолевого процесса. При биохимическом тестировании крови отмечалось незначительное повышение уровня прямого билирубина и сывороточного железа. Для уточнения диагноза проведена магнитно-резонансная томография органов малого таза с внутривенным контрастированием. После проведения указанного обследования был выставлен диагноз "кистозное образование правого яичка". После проведения необходимых дополнительных диагностических мероприятий (УЗИ периферических лимфатических узлов, обследование брюшной полости с внутривенным контрастным усилением) выполнена операция, заключавшаяся в ревизии правой половины мошонки и удалении образования правого яичка. Интраоперационно по данным экспресс-биопсии диагностировалась дермоидная киста правого яичка, что подтвердилось при последующем гистологическом исследовании. Послеоперационный период протекал гладко. Пациент выписался в удовлетворительном состоянии. Таким образом, представленное клиническое наблюдение подчеркивает необходимость оптимизации профилактической работы медицинского персонала первичного звена по своевременной диагностике опухолевых процессов наружных половых органов, особенно у детей пубертатного возраста.The paper presents a clinical case of a 14-year-old child with a dermoid cyst of the right testicle. The formation was first detected during a routine check-up in the polyclinic. Then the external genitalia ultrasound examination was repeatedly performed to the patient, which revealed an inhomogeneous echostructure with dimensions of 14 mm, 13.7 mm and 12 mm with a clear, even contour in the upper pole of the right testicle. The enzyme-linked immunosorbent assay (ELISA) did not show an increase in the main tumour markers. The biochemical blood test revealed an insignificant rise in conjugated bilirubin and serum iron. To clarify the diagnosis, magnetic resonance tomography of the pelvic organs with intravenous contrast was recommended. After examination, the cystic lesion of the right testicle was diagnosed. After carrying out the necessary additional diagnostic measures (ultrasound examination of the peripheral lymphatic nodes, the abdominal cavity exploration with intravenous contrast enhancement), the child underwent an operation consisting in revising the right half of the scrotum and removing the formation of the right testicle. Intraoperatively, according to the express biopsy test, the dermoid cyst of the right testicle was diagnosed, which was confirmed by the subsequent histological examination. The postoperative period was uneventful. The patient was discharged in satisfactory state. Thus, the presented clinical observation emphasizes the need to optimize the preventive work of primary care medical personnel for timely diagnosis of tumor processes in the external genital organs, especially in children of puberty

High order fluid model for streamer discharges

A high order fluid model for streamer discharges is developed and used to investigate propagation of negative streamer fronts in N2 . Mo- mentum transfer theory is employed to evaluate the collision terms and close the system of moment/balance equations. The results of simulations are compared with those obtained by a PIC/MC method and by the classical first order fluid model based on the drif

Peculiarities of a Colloidal Polysaccharide of Newly Isolated Iron Oxidizing Bacteria in Armenia

Microorganisms belonging to different systematic and physiological groups produce various intra- and extracellular polysaccharides, which both play an important role in the life of microorganisms and have great practical application. Iron and sulfur oxidizing bacteria produce capsular (EPS) and colloidal polysaccharides. At present the properties and functional role of EPS are well studied. However, the properties of the colloidal polysaccharides produced by iron oxidizing bacteria have not been sufficiently explored. A new iron oxidizing bacteria Leptospirillum ferriphilium CC was isolated from sulfide ores of Armenia. Its morphological and physiological features have been studied. A colloidal polysaccharide has been isolated with the use of an original method developed by the authors, and its physical and chemical properties have been studied. It has been shown that the colloidal polysaccharide consists of three different monomers- glucose, fructose, mannose.. Investigations with a complex method of optical polarization microscopy and analytical programs allowed determining the size, shape change, perimeter, degree of hydratation and crystallization at 0.07% and 0.04% of polysaccharide concentration. It was shown that the size of a polysaccharide colloidal particle does not much depend on polysaccharide concentration, however, the number of identical colloidal formations is dependent on the concentration of polysaccharide