The effect of the stochasticity of photoionization on 3D streamer simulations

Positive streamer discharges require a source of free electrons ahead of them for their growth. In air, these electrons are typically provided by photoionization. Here we investigate how stochastic fluctuations due to the discreteness of ionizing photons affect positive streamers in air. We simulate positive streamers between two planar electrodes with a 3D plasma fluid model, using both a stochastic and a continuum method for photoionization. With stochastic photoionization, fluctuations are visible in the streamer's direction, maximal electric field, velocity, and electron density. The streamers do not branch, and we find good agreement between the averaged stochastic results and the results with continuum photoionization. The streamers stay roughly axisymmetric, and we show that results obtained with an axisymmetric model indeed agree well with the 3D results. However, we find that positive streamers are sensitive to the amount of photoionization. When the amount of photoionization is doubled, there is even better agreement between the stochastic and continuum results, but with half the amount of photoionization, stochastic fluctuations become more important and streamer branching starts to occur

Study of the antibacterial activity of total extract and Petroleum ether, chloroform, ethyl acetate and aqueous fractions of aerial parts of heliotropium bacciferum against staphylococcus aureus, Bacillus cereus, Pseudomonas aeruginosa, E.coli, Salmonella enteritidis

Heliotropium bacciferum is One of the plants belonging to the family Boraginaceae , which is Restricted distribution in the south of Iran. It is used for Hypotension, fever, stomach ulcers in traditional medicine. In this study, the antibacterial effects of extracts and fractions of chloroform, ethyl acetate and aqueous, aerial parts of Heliotropium bacciferum Forssk was evaluated against five bacterial strains. The methanol extract were prepared using the percolation method. Fractions of chloroform, Petroleum ether, ethyl acetate, methanol and aqueous respectively by Liquid - Liquid fractionation of the total extract were prepared. The antibacterial activity against two Gram positive bacteria, three Gram negative bacterial using Minimum inhibitory concentration in microplate and well plate method. Results showed that H. bacciferum extracts exhibited a significant activity against strains Staphylococcus aureus, Bacillus cereus,Pseudomonas aeruginosa, E.coli, Salmonella enteritidis. MIC and well plate is between 7.6-125 μg/ml. The results of this study indicate that extracts of the plant H.bacciferum has a antimicrobial effect against strains are listed And among the extracts, aqueous part is that most antibacterial effect of the other fraction and then methanolic extract has the greatest effect

Application of Whole-body Vibration: Technical and clinical studies in healthy persons and people with a neurological disorder

__Abstract__ The first use of vibration therapy to improve human fimction and muscle performance dates back to ancient Greece, a time when physicians used saws covered in cotton to transfer vibrations to specific parts of the body to improve muscle performance and relieve pain. However, these manual devices could only offer vibration locally and in one direction. It was not until the middle of the 19th century that physicians developed machines which produced both vertical and circular movements, which were considered to treat disorders such as neuralgia, muscular atrophy, emaciation and constipation1· 3. In 1880, the French neurologist Jean-Martin Charcot examined the surprising improvements in the condition of pilgrims suffering from Parkinson's disease. He surmised that such improvements were attributable to the vibration from the horse-drawn and railway carriages. Based on this idea he developed a chair with a helmet that vibrated electrically. Between 1890 and 1910, Charcot's ideas were further developed by various therapists. In 1960, the West German Dr. Biermann published the paper Influence of cycloid vibration massage on trunk flexion in the American Journal of Physical Medicine4• Since 1970, Professor Vladimir Nazarov developed a vibration training program as an effective method for athletes. Using Biermann's ideas, he observed an improvement in power and flexibility in practical exercises. A little later, this local vibration training was used by the Russians in their space program to prevent bone density changes in astronauts. They recognized that this new idea for exercise had the potential to provide suitable countermeasures for preventing bone and muscle loss for astronauts under micro gravity conditions. Whole-body vibration (WBV) was later used to enhance the performance of Soviet athletes during their exercise training5 • However, the Russians kept the technology secret until after the Berlin Wall came down inN ovember 1989. Since 1990, the European Space Agency and NASA also used vibration technology in ongoing studies on the maintenance of muscle strength, mass, and bone density. Simultaneously, extensive research was started on WBV in other areas ofthe world. In 1999, the Dutch Olympic coach, Guus van de Meer, introduced vibration training technology in Western Europe. He introduced a new way ofWBV application, with emphasis on optimizing natural human fimction while preserving joint health and maximizing power. Nowadays, there is increasing interest in the use ofWBV as a therapeutic modality to improve muscle strength, postural stability, and to increase bone density in groups of people of different types and ages

Stomach contents of Mnemiopsis leidyi in the Iranian coastal waters of the Caspian Sea

This study was carried out from August to November 2002 in the Iranian coastal waters of the Caspian Sea (Guilan province). The results showed that gut contents of Mnemiopsis leidyi included a wide variety of prey including 84% of zooplanktons and 16% of phytoplanktons. The most abundance of intaked foods was Acartia (belongs to Copepoda) with 34% frequency and the least was podon (belongs to Cladocera) with 0.74% frequency. Also 3.0% of fish eggs and 4.2% of molluscs were found among stomach contents. Maximum and minimum fed phytoplanktons were Chrysophyta (67.0%) and Pyrrophyta (3.7%), respectively. The young specimen consumed more zooplanktons and phytoplanktons comparing to adult ones. According to laboratory observations, this ctenophore cannot digest phytoplanktons

Environmental, developmental, and genetic factors controlling root system architecture

A better understanding of the development and architecture of roots is essential to develop strategies to increase crop yield and optimize agricultural land use. Roots control nutrient and water uptake, provide anchoring and mechanical support and can serve as important storage organs. Root growth and development is under tight genetic control and modulated by developmental cues including plant hormones and the environment. This review focuses on root architecture and its diversity and the role of environment, nutrient, and water as well as plant hormones and their interactions in shaping root architecture

Quantitative performance metrics for robustness in circadian rhythms

Motivation: Sensitivity analysis provides key measures that aid in unraveling the design principles responsible for the robust performance of biological networks. Such metrics allow researchers to investigate comprehensively model performance, to develop more realistic models, and to design informative experiments. However, sensitivity analysis of oscillatory systems focuses on period and amplitude characteristics, while biologically relevant effects on phase are neglected. Results: Here, we introduce a novel set of phase-based sensitivity metrics for performance: period, phase, corrected phase and relative phase. Both state- and phase-based tools are applied to free-running Drosophila melanogaster and Mus musculus circadian models. Each metric produces unique sensitivity values used to rank parameters from least to most sensitive. Similarities among the resulting rank distributions strongly suggest a conservation of sensitivity with respect to parameter function and type. A consistent result, for instance, is that model performance of biological oscillators is more sensitive to global parameters than local (i.e. circadian specific) parameters. Discrepancies among these distributions highlight the individual metrics' definition of performance as specific parametric sensitivity values depend on the defined metric, or output. Availability: An implementation of the algorithm in MATLAB (Mathworks, Inc.) is available from the authors. Contact: [email protected] Supplementary information: Supplementary Data are available at Bioinformatics onlin