670 research outputs found

    The effect of Studying Morphology in Modeling Syntactic concepts in the lessons of the native Language in Primary Grades

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    The article is about how to improve the methodology of teaching the mother tongue and activate students' motivation to acquire knowledge and skills in the lessons of their mother tongue by modeling syntactic concepts in the lessons of their mother tongu

    Ion energy and angular distributions onto polymer surfaces delivered by dielectric barrier discharge filaments in air: II. Particles

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    Atmospheric pressure streamers intersecting particles are of interest in the context of plasma aided combustion, where the particle may be a fuel aerosol droplet, or in sterilization of air, where the particle may be a bacterium. The ion energy and angular distributions (IEADs) incident on the particles, small curved dielectric surfaces, then in part determine the propensity for activating chemical reactions or, in the case of bacteria, the plasma's sterilization capability. In this paper, we discuss results from a computational investigation of IEADs on small particles (45 µm radius) produced by atmospheric pressure discharge. Streamers intersecting a particle momentarily generate a large sheath potential as the streamer passes by as the particle charges towards the plasma floating potential. During that time, ions of energies up to 3–10 eV can strike the particle. The permittivity of the particle and the streamer polarity in part determine the character of the IEAD.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90808/1/0963-0252_20_3_035018.pd

    Ion energy and angular distributions onto polymer surfaces delivered by dielectric barrier discharge filaments in air: I. Flat surfaces

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    In atmospheric pressure discharges, ion energies are typically thought to be thermal with values dominantly <1 eV. In the heads of filaments in dielectric barrier discharges (DBDs), electric fields can exceed 200 kV cm _1 when the filament is far from a surface. As the filament approaches and intersects a dielectric surface, much of the applied potential is compressed into the voltage drop across the head of the filament due to the high conductivity of the trailing plasma channel. When the filament strikes the surface, this voltage is transferred to the resulting sheath and into the material of the surface. The degree of electric field compression depends on the dielectric constant _/_ 0 of the surface. Upon intersection of the filament with the surface, the electric fields in the resulting sheath can exceed 400–800 kV cm _1 , with larger values corresponding to larger _/_ 0 . When accelerated in these fields, ions can gain energies across their mean free path (0.5–1 µm) up to 20 eV for dielectrics with low _/_ 0 and up to 150 eV for dielectrics with high _/_ 0 , albeit only for the duration of the intersection of the streamer with the surface of a few ns. In this paper we report on results from a computational investigation of the ion energy and angular distributions (IEADs) incident on dielectric flat surfaces resulting from the intersection of DBD filaments sustained in atmospheric pressure air. We describe the transient and spatially dependent IEADs as the filament spreads across the polymer.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90807/1/0963-0252_20_3_035017.pd

    Intracellular electric fields produced by dielectric barrier discharge treatment of skin

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    The application of atmospheric pressure plasmas to human tissue has been shown to have therapeutic effects for wound healing and in treatment of skin diseases. These effects are attributed to both production of beneficial radicals which intersect with biological reaction chains and to the surface and intracellular generation of electric fields. In this paper, we report on computational studies of the intersection of plasma streamers in atmospheric pressure dielectric barrier discharges (DBDs) sustained in air with human skin tissue, with emphasis on the intracellular generation of electric fields. Intracellular structures and their electrical properties were incorporated into the computational mesh in order to self-consistently couple gas phase plasma transport with the charging of the surface of the skin and the intracellular production of electrical currents. The short duration of a single plasma filament in DBDs and its intersection with skin enables the intracellular penetration of electric fields. The magnitude of these electric fields can reach 100 kV cm−1 which may exceed the threshold for electroporation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85408/1/d10_18_185206.pd

    Effect of inhomogeneities on streamer propagation: I. Intersection with isolated bubbles and particles

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    The branching of streamers in high pressure gas discharges and discharges in liquids is an almost universal occurrence having many causes. In this paper, we discuss results of an investigation of one possible cause inhomogeneities in the media through which the streamer propagates. These inhomogeneities produce corresponding enhancements or decreases in ionization and excitation as the avalanche front encounters them, some of which may produce branching. Three types of inhomogeneities were investigated negative bubbles (regions having a lower density than ambient), positive bubbles (having a higher density) and solid bubbles (particles). Depending on the size and density of the bubble, the streamer can be focused into the bubble (negative small bubble), deflected and split (positive bubbles and particles) or refracted (large negative bubble). In the case of gaseous bubbles, this behavior is partly explained by the larger E / N (electric field/gas number density) in the negative bubble, producing more ionization by electron avalanche, and smaller E / N in the positive bubble, producing less ionization. A streamer may diverge into a negative bubble located off axis due to seeding of electrons in the bubble by photoionization and subsequent avalanching in the large E / N .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65091/2/psst9_3_035009.pd

    Structure of positive streamers inside gaseous bubbles immersed in liquids

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    Electric discharges and streamers in liquids typically proceed through vapour phase channels produced by the streamer or in gaseous bubbles. The bubbles can originate by enthalpy changes produced by the discharge or can be artificially injected into the liquid. Experiments on streamers in bubbles immersed in liquids have shown that the discharge propagates either along the surface of the bubble or through the volume of the bubble as in conventional streamer propagation in air. In this paper we report on results of a computational investigation of streamer propagation through bubbles immersed in liquids. We found that the dielectric constant of the liquid in large part determines the path the streamer takes. Streamers in bubbles immersed in a liquid with a high permittivity preferentially propagate along the surface of the bubble. Liquids with low permittivity can result in the streamer propagating along the axis of the bubble. The permittivity at which this transition occurs is a function of the applied voltage, size of the bubble and the conductivity of the liquid.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65086/2/d9_13_132003.pd

    The Importance of L.S. Vygotsky’s and A.R. Luria’s Ideas in the Study of ‘Twice Exceptional’ Children

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    The article highlights the importance of ‘twice exceptionality’ studies and the significance of L.S. Vygotsky and A.R. Luria’s ideas for this research. Twice exceptional children combine the signs of giftedness with one or several mental disabilities, specific learning difficulties, etc. In our research, we analyzed the developmentof writing skills in three groups of school children with different variants of mental functions development, distinguished on the basis of neuropsychological characteristics. The use of the original method of recording movements while writing, combined with a neuropsychological assessment of children allowed revealing the dependence of writing parameters and their dynamics on the strength and weakness of the components involved in the functional system of writing. According to the results obtained, each group has its own pattern of the following parameters: time, writing quality and errors, explained by the primary weakness in the child’sfunctional system of writing and compensatory restructuring. A comparative analysis of analytical and holistic strategies use in reading was also conducted. Keywords: ‘twice-exceptional children’, mental functions development desynchrony, neuropsychological analysis, difficulties and specific errors in writing

    Effect of inhomogeneities on streamer propagation: II. Streamer dynamics in high pressure humid air with bubbles

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    The branching of electric discharge streamers in atmospheric pressure air, dense gases and liquids is a common occurrence whose origins are likely found with many causes, both deterministic and stochastic. One mechanism for streamer branching may be inhomogeneities in the path of a streamer which either divert the streamer (typically a region of lower ionization) or produce a new branch (a region of higher ionization). The propagation and branching of streamers in liquids is likely aided by low density inhomogeneities, bubbles; however, modeling of streamers in liquids is made difficult by the lack of transport coefficients. As a first step towards understanding the propagation and branching of streamers in liquids, we investigated the consequences of random inhomogeneities in the form of low pressure bubbles on the propagation of streamers in high pressure humid air. By virtue of their lower density, bubbles have larger E / N (electric field/gas number density) than the ambient gas with larger rates of ionization. The intersection of a streamer with a bubble will focus the plasma into the bubble by virtue of that higher rate of ionization but the details of the interaction depend on the relative sizes of the bubble and streamer. When a streamer intersects a field of bubbles, the large E / N in the bubble avalanches seed electrons produced by photoionization from the streamer. Each bubble then launches both a negative and positive going streamer that may link with those from adjacent bubbles or the original streamer. The total process then appears as streamer branching.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65096/2/psst9_3_035010.pd

    Pharmacognostical study of achenes of some plants from Asteraceae family

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    In the present paper are represented morphological studies on determination of weight of 1000 achenes, and sieve analysis of fruits of some plants from Asteraceae family (Arctium lappa L., Leuzea carthamoides (Willd.) D.C, Inula helenium L., Echinacea purpurea Moench., Calendula officinalis L.). Lipid, alcohol-soluble and water-soluble complexes in fruits of C. officinalis were studied

    Mineral Resources of the Ocean: a Pragmatical Reality of the Foreseeable Future or Geopolitical Phantom

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    Изложено состояние изученности твердых полезных ископаемых Мирового океана (ЖМК, КМК, ГПС), дана оценка возможного вклада в минерально-сырьевую базу страны. Отмечается, что проблема минеральных ресурсов океана уже в обозримом будущем может иметь не только геополитическое, но и реальное практическое значение.The study is dedicated to the state of knowledge of the oceanic minerals (FMN, CMC, DSPS) and estimation of their possible contribution to the raw materials base of the Country. The problem of oceanic mineral resources may have not only geopolitical, but also practical value in the foreseeable futur
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