Non-Maxwellian velocity distribution functions associated with steep temperature gradients in the solar transition region. Paper 2: The effect of non-Maxwellian electron distribution functions on ionization equilibrium calculations for carbon, nitrogen and oxygen

Non-Maxwellian electron velocity distribution functions, previously computed for Dupree's model of the solar transition region are used to calculate ionization rates for ions of carbon, nitrogen, and oxygen. Ionization equilibrium populations for these ions are then computed and compared with similar calculations assuming Maxwellian distribution functions for the electrons. The results show that the ion populations change (compared to the values computed with a Maxwellian) in some cases by several orders of magnitude depending on the ion and its temperature of formation

Non-Maxwellian velocity distribution functions associated with steep temperature gradients in the solar transition region. Paper 1: Estimate of the electron velocity distribution functions

It was shown that, in the presence of the steep temperature gradients characteristic of EUV models of the solar transition region, the electron and proton velocity distribution functions are non-Maxwellian and are characterized by high energy tails. The magnitude of these tails are estimated for a model of the transition region and the heat flux is calculated at a maximum of 30 percent greater than predicted by collision-dominated theory

Relating porous media structure to the Darcy-Forchheimer model

Flow in porous media is an important aspect of many systems, such as fluid separation, heat exchange, underground fluid transport, filtration, and purification. Computational modeling is used in all of these systems to increase the understanding of the system and enable researchers to make optimal decisions regarding the processes within the system. Current tools for modeling flow in porous media require calibration of each system individually, which reduces the quantity and efficiency of the information that simulations can provide. The most common method for modeling flow in porous media, is the Darcy-Forchheimer model. Although this model is accurate and robust, it relies on two coefficients which can only be determined through physical experiments on each individual porous media. These coefficients can be expressed as a product of the fluid properties and the properties of porous media structure; however the variables representing the structure of the porous media are still unable to be determined without physical experiments. For many years determining the relationship between porous media structure and the Darcy-Forchheimer model has been considered impractical, because the scale of porous media made it difficult if not impossible to measure the geometric properties of the material. Additionally, naturally occurring porous media have random structures; thus even if it were feasible to measure the porous media, it would have been difficult to determine the characteristics that most affect flow. Now researchers can both measure and manufacture porous media for specific purposes; however the models have not been updated to allow researchers to take advantage of this technology. Although researchers have the ability to control the exact structure of porous media, the models still lack the ability to help researchers create optimal designs for their systems. This research focuses on understanding the fundamental dynamics of flow in porous media, to enable complex systems to be modeled and developed more easily. Here computational upscaling is used to develop a revised Darcy-Forchheimer equation which includes a relation to the parameters of the porous media. The revised model was developed by simulating several homogeneous structured porous media. The porous media were studied by simulating a periodic unit cell of each porous media to understand the geometric effects. A primary porous media, made of stacked screens was used for the initial analysis. This porous media could be described in as little as two parameters, allowing multiple analyses to be completed without consideration of previous knowledge regarding how flow should behave in porous media. This analysis supported the long held assumption that the Darcy-Forchheimer equation can be divided into a viscous loss term and an inertial loss term. After this primary analysis several less ideal porous media were modeled and analyzed similar to the primary case. A more general relationship that can be used for a wide variety of homogeneous porous media was developed

HYDROFLASH: A 2-D Nuclear EMP Code Founded on Finite Volume Techniques

The basic mechanisms that govern the generation of an electromagnetic pulse (EMP) following a nuclear detonation in the atmosphere, including heights of burst (HOB) relevant to surface bursts (0 km), near surface bursts (0-2 km), air bursts (2-20 km) and high-altitude bursts (> 20 km), are reviewed. Previous computational codes developed to treat the source region and predict the EMP are discussed. A new 2-D hydrodynamic code (HYDROFLASH) that solves the fluid equations for electron and ion transport in the atmosphere and the coupled Maxwell equations using algorithms extracted from the Conservation Law (CLAW) package for solving multi-dimensional hyperbolic equations with finite volume techniques has been formulated. Simulations include the ground, atmospheric gradient, and an azimuthal applied magnetic field as a first approximation to the geomagnetic field. HYDROFLASH takes advantage of multiprocessor systems by using domain decomposition together with the Message Passing Interface (MPI) protocol for parallel processing. A detailed description of the model is presented along with computational results for a generic 10 kiloton (kT) burst detonated at 0 and 10 km altitude

Nonlinear whistler wave scattering in space plasmas

In this paper the evolution of nonlinear scattering of whistler mode waves by kinetic Alfven waves (KAW) in time and two spatial dimensions is studied analytically. The authors suggest this nonlinear process as a mechanism of kinetic Alfven wave generation in space plasmas. This mechanism can explain the dependence of Alfven wave generation on whistler waves observed in magnetospheric and ionospheric plasmas. The observational data show a dependence for the generation of long periodic pulsations Pc5 on whistler wave excitation in the auroral and subauroral zone of the magnetosphere. This dependence was first observed by Ondoh T.I. For 79 cases of VLF wave excitation registered by Ondoh at College Observatory (L=64.6 N), 52 of them were followed by Pc5 geomagnetic pulsation generation. Similar results were obtained at the Loparskaia Observatory (L=64 N) for auroral and subauroral zone of the magnetosphere. Thus, in 95% of the cases when VLF wave excitation occurred the generation of long periodic geomagnetic pulsations Pc5 were observed. The observations also show that geomagnetic pulsations Pc5 are excited simultaneously or insignificantly later than VLF waves. In fact these two phenomena are associated genetically: the excitation of VLF waves leads to the generation of geomagnetic pulsations Pc5. The observations show intensive generation of geomagnetic pulsations during thunderstorms. Using an electromagnetic noise monitoring system covering the ULF range (0.01-10 Hz) A.S. Fraser-Smith observed intensive ULF electromagnetic wave during a large thunderstorm near the San-Francisco Bay area on September 23, 1990. According to this data the most significant amplification in ULF wave activity was observed for waves with a frequency of 0.01 Hz and it is entirely possible that stronger enhancements would have been measured at lower frequencies

Video and Photometric Observations of a Sprite in Coincidence with a Meteor-triggered Jet Event

Video and photometric observations of a meteor-triggered “jet” event in association with the occurrence of a sprite were collected during the SPRITES \u2798 campaign. The event raises interest in the question of possible meteoric triggering of upper atmospheric transients as originally suggested by Muller [1995]. The event consisted of three stages: (1) the observation of a moderately bright meteor, (2) the development of a sprite in the immediate vicinity of the meteor as the meteor reached no lower than ∼70 km altitude, and (3) a slower-forming jet of luminosity that appeared during the late stages of the sprite and propagated back up the ionization trail of the meteor. The event is analyzed in terms of its geometry, its relevance to the meteor, and the implications to existing theories for sprite formation

Synthesis of hierarchical wo3 microspheres for photoelectrochemical water splitting application

In this work, hierarchical WO3 microspheres were synthesized using chemical bath deposition. The morphology of the synthesized sample was studied using scanning electron microscopy (SEM). The hierarchical WO3 microspheres formed from spontaneously self-assembled nanosheets have a high specific surface area. Structural characterizations of sample were performed using X-ray diffraction (XRD) and Raman spectroscopy. Analysis of XRD spectra showed that synthesized particles have a monoclinic modification. The optical properties of the sample were studied using UV-Vis diffuse reflectance absorption spectra. The value of the energy gap calculated from the absorption spectra is 2.2 eV, which indicates high light absorption ability. A photocurrent study was done to investigate the photocatalytic activity. The photoelectrode was prepared using hierarchical WO3 microspheres and polymer deposited on fluorine doped tin oxide (FTO) glass via spin coating technique. A remarkable photocurrent density of 18 A/cm2 at 0.5 V was achieved. The elongated structures improved light absorption ability and photocatalytic activity

HF echoes from ionization potentially produced by high-altitude discharges

In this paper the authors report on recent radar measurements taken during the month of October 1994 with the LDG HF radar in the Ivory Coast, Africa as part of the International Equatorial Electrojet Year. The purpose of this experimental effort in part was to study the effects of thunderstorms on the ionosphere. At the same time, the authors decided to carry out a set of experiments of an exploratory nature to look for echoes that could potentially arise from ionization produced in the mesosphere. The two leading candidates for producing transient ionization in the mesosphere are meteors and high-altitude discharges. Each is discussed in the context of these measurements