A comparison of 3D particle, fluid and hybrid simulations for negative streamers

In the high field region at the head of a discharge streamer, the electron energy distribution develops a long tail. In negative streamers, these electrons can run away and contribute to energetic processes such as terrestrial gamma-ray and electron flashes. Moreover, electron density fluctuations can accelerate streamer branching. To track energies and locations of single electrons in relevant regions, we have developed a 3D hybrid model that couples a particle model in the region of high fields and low electron densities with a fluid model in the rest of the domain. Here we validate our 3D hybrid model on a 3D (super-)particle model for negative streamers in overvolted gaps, and we show that it almost reaches the computational efficiency of a 3D fluid model. We also show that the extended fluid model approximates the particle and the hybrid model well until stochastic fluctuations become important, while the classical fluid model underestimates velocities and ionization densities. We compare density fluctuations and the onset of branching between the models, and we compare the front velocities with an analytical approximation

RELATIONS FOR CALCULATING THERMODYNAMIC AND TRANSPORT PROPERTIES OF LIQUID LITHIUM

The results of the analysis of experimental data from open publications for the period from 1933 to 2018 are presented. The calculated relations for estimating the density,heat ca-pacity,thermal conductivity,dynamic viscosity,surface tension,and electrical resistivity for liquid lithium are proposed

Positive and negative streamers in ambient air: modeling evolution and velocities

We simulate short positive and negative streamers in air at standard temperature and pressure. They evolve in homogeneous electric fields or emerge from needle electrodes with voltages of 10 to 20 kV. The streamer velocity at given streamer length depends only weakly on the initial ionization seed, except in the case of negative streamers in homogeneous fields. We characterize the streamers by length, head radius, head charge and field enhancement. We show that the velocity of positive streamers is mainly determined by their radius and in quantitative agreement with recent experimental results both for radius and velocity. The velocity of negative streamers is dominated by electron drift in the enhanced field; in the low local fields of the present simulations, it is little influenced by photo-ionization. Though negative streamer fronts always move at least with the electron drift velocity in the local field, this drift motion broadens the streamer head, decreases the field enhancement and ultimately leads to slower propagation or even extinction of the negative streamer.Comment: 18 pages, 10 figure

Apokamps produced by repetitive discharges in air

New experimental and computational data on apokamps produced by repetitive discharges in air, including a detailed description of the research techniques used, are presented. It has been shown that plasma bullets–streamers in apokamps at low frequencies could start not only from the bright offshoot but also directly from the discharge channel. The experimental and computational data demonstrate that the visual color of apokamp changes from blue to red as the intensity ratio of the second to the first positive nitrogen system decreases with the decreasing pressure

Transforming growth factor β1 (TGF-β1) in patients with endocrine ophthalmopathy and Graves’ disease: A predictor of treatment efficiency

Current therapeutic approaches to the treatment of endocrine ophthalmopathy (EOP) are based on nonspecific immunosuppression with glucocorticosteroids (GCs) and radiation therapy of the eye orbits. However, some patients exhibit resistance to the treatment. In a previous study, we have detected high levels of soluble cytokine receptors: sTNFα-R1, sTNFα-R2, sIL-2R, and the TGF-β1 cytokine in euthyroid patients with long-lasting non-treated EOP and Graves’ disease (GD). TGF-β1 level was significantly higher in the patients with EOP compared to healthy individuals, and increased with prolonged EOP duration, thus suggesting activation of the factors regulating immune system which promote suppression of the autoimmune process. The aim of this work was to study the dynamics of TGF-β1 and cytokine receptors: sTNFα-R1, sTNFα-R2, sIL-2R in the course of immunosuppressive therapy with high doses of GCs, as possible predictors of treatment efficacy. The study included 49 patients (98 eye orbits) with GD of euthyroid state and subclinical thyrotoxicosis, and the persons with EOP in active phase, who had not previously treatment for EOP. Concentrations of TGF-β1 cytokine, sTNFα-RI and sTNFα-R2, sIL-2R, antibodies to the thyroid-stimulating hormone receptor (rTSH), free fractions of thyroxine (fT4) and triiodothyronine (fT3), TSH in blood serum were determined in blood serum. Ultrasound examination of the thyroid gland (ultrasound of the thyroid gland), multi-layer computed tomography (MSCT)/magnetic resonance imaging (MRI) of the orbits were also performed. The patients were administered immunosuppressive therapy with high doses of HCs (methylprednisolone) in the course of pulse therapy, at a standard dosage of 4500-8000 mg, taking into account the severity and activity of the EOP clinical manifestations. The examination was carried out 3, 6, 12 months after starting the treatment. 3 and 6 months after the GC administration, more than 30% of patients remained resistant to treatment. The levels of TGF-β1 did not change significantly in the patients with positive EOP dynamics. In the patients resistant to GC treatment, the level of TGF-β1 was significantly decreased compared with patients who showed positive clinical dynamics. The level of sNFR1 and sNFaR2 did not change significantly. There were no significant differences in the levels of antibodies to rTSH, thyroid hormones in the patients resistant to GC treatment and with positive dynamics.Immunosuppressive therapy with high-dose of methylprednisolone in pulse therapy regimen showed high efficacy and good tolerability, while some patients remain resistant to treatment. Lower levels of TGF-β1 cytokine at initial time and during the treatment allow usage of TGF-β1 levels as a biomarker of the activity of the process, treatment efficiency, and prognosis of the disease. Activation of TGF-β1, a fibroblast growth factor, may contribute to the development of fibrosis, strabismus, and diplopia

Simulation of the discharge propagation in a capillary tube in air at atmospheric pressure

International audienceThis paper presents simulations of an air plasma discharge at atmospheric pressure initiated by a needle anode set inside a dielectric capillary tube. We have studied the influence of the tube inner radius and its relative permittivity ε r on the discharge structure and dynamics. As a reference, we have used a relative permittivity ε r = 1 to study only the influence of the cylindrical constraint of the tube on the discharge. For a tube radius of 100 µm and ε r = 1, we have shown that the discharge fills the tube during its propagation and is rather homogeneous behind the discharge front. When the radius of the tube is in the range 300 to 600 µm, the discharge structure is tubular with peak values of electric field and electron density close to the dielectric surface. When the radius of the tube is larger than 700 µm, the tube has no influence on the discharge which propagates axially. For a tube radius of 100 µm, when ε r increases from 1 to 10, the discharge structure becomes tubular. We have noted that the velocity of propagation of the discharge in the tube increases when the front is more homogeneous and then, the discharge velocity increases with the decrease of the tube radius and ε r. Then, we have compared the relative influence of the value of tube radius and ε r on the discharge characteristics. Our simulations indicate that the geometrical constraint of the cylindrical tube has more influence than the value of ε r on the discharge structure and dynamics. Finally, we have studied the influence of photoemission processes on the discharge structure by varying the photoemission coefficient. As expected, we have shown that photoemission, as it increases the number of secondary electrons close to the dielectric surface, promotes the tubular structure of the discharge

Age-related determinants of the metabolic syndrome in women of reproductive age of the main ethnic groups of the Baikal Region

The aim of the study. To determine the age limit of the initial manifestations of the metabolic syndrome in women of reproductive age of the Caucasian and Asian ethnic groups. Materials and methods. The study included women of reproductive age of the Russian and Buryat ethnic groups (n = 1231). We carried out general clinical examination, studied glycemia levels and lipid metabolism indicators. The analysis of the components of the metabolic syndrome was performed taking into account age characteristics and ethnicity. Threshold values for the age of metabolic disorders manifestation were determined. Results. It was found that the main components of the metabolic syndrome in women of reproductive age of the Russian and Buryat ethnic groups were a decrease in  high-density lipoprotein (HDL), an increase in waist circumference, and an increase in blood pressure. The age-related determinants of the metabolic syndrome in the  population of women of reproductive age in the Baikal region were determined. It was shown that the age-related determinants of the metabolic syndrome in Caucasian and Asian women do not differ significantly and amount to 33.5 years (95% confidence interval (95% CI): 32.5; 38.5) and 36.5 years (95% CI: 27.5; 52.5), respectively. A universal critical age value was determined as 34.5 years (95% CI: 32.5; 38.5), which is associated with a significant increase in the prevalence of the metabolic syndrome in accordance with the ATP  III criteria. The ranking of metabolic syndrome criteria in the studied groups revealed the following order of their occurrence: the decrease in HDL index prevailed, followed by the increase in waist circumference, blood pressure, glucose and triglycerides; no dependence on the ethnicity was found. Conclusion. When assessing the age-related determinants of the metabolic syndrome in the mixed Caucasoid-Asian group, it is advisable to use universal approaches, taking into account the cut-off point of age, which is 34.5 years. The determination of age criteria for the correct classification of patients with respect to the manifestations of the metabolic syndrome is necessary to analyze the contribution of the age factor to the implementation of various metabolic syndrome predictors, to  develop prognostic models, and to  use effective age-determined markers of metabolic disorders