Ionization in fast atom-atom collisions: The influence and scaling behavior of electron-electron and electron-nucleus interactions

We report cross sections for ionization of He coincident with electron loss from He, Li, C, O, and Ne projectiles. For He, Li, C, and O projectiles, the cross sections were measured directly, while the Ne cross sections were obtained by transforming results for He projectiles colliding with Ne. We find that, at energies of about 100–500 keV/u, neutral projectiles can ionize a He target almost as effectively as a charged projectile. The contribution to ionization due to electron-electron interactions is found to scale with the number of available projectile electrons. Comparing ionization by the bound electrons on projectiles to ionization by free electrons, we find that the cross sections for ionization by bound electrons are systematically smaller than those for free electrons

Photonuclear fission with quasimonoenergetic electron beams from laser wakefields

Recent advancements in laser wakefield accelerators have resulted in the generation of low divergence, hundred MeV, quasimonoenergetic electron beams. The bremsstrahlung produced by these highly energetic electrons in heavy converters includes a large number of MeV γγ rays that have been utilized to induce photofission in natural uranium. Analysis of the measured delayed γγ emission demonstrates production of greater than 3×1053×105 fission events per joule of laser energy, which is more than an order of magnitude greater than that previously achieved. Monte Carlo simulations model the generated bremsstrahlung spectrum and compare photofission yields as a function of target depth and incident electron energy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87815/2/231107_1.pd

A light-fronts approach to electron-positron pair production in ultrarelativistic heavy-ion collisions

We perform a gauge-transformation on the time-dependent Dirac equation describing the evolution of an electron in a heavy-ion collision to remove the explicit dependence on the long-range part of the interaction. We solve, in an ultra-relativistic limit, the gauged-transformed Dirac equation using light-front variables and a light-fronts representation, obtaining non-perturbative results for the free pair-creation amplitudes in the collider frame. Our result reproduces the result of second-order perturbation theory in the small charge limit while non-perturbative effects arise for realistic charges of the ions.Comment: 39 pages, Revtex, 7 figures, submitted to PR

Cloud type comparisons of AIRS, CloudSat, and CALIPSO cloud height and amount

The precision of the two-layer cloud height fields derived from the Atmospheric Infrared Sounder (AIRS) is explored and quantified for a five-day set of observations. Coincident profiles of vertical cloud structure by CloudSat, a 94 GHz profiling radar, and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), are compared to AIRS for a wide range of cloud types. Bias and variability in cloud height differences are shown to have dependence on cloud type, height, and amount, as well as whether CloudSat or CALIPSO is used as the comparison standard. The CloudSat-AIRS biases and variability range from −4.3 to 0.5±1.2–3.6 km for all cloud types. Likewise, the CALIPSO-AIRS biases range from 0.6–3.0±1.2–3.6 km (−5.8 to −0.2±0.5–2.7 km) for clouds ≥7 km (<7 km). The upper layer of AIRS has the greatest sensitivity to Altocumulus, Altostratus, Cirrus, Cumulonimbus, and Nimbostratus, whereas the lower layer has the greatest sensitivity to Cumulus and Stratocumulus. Although the bias and variability generally decrease with increasing cloud amount, the ability of AIRS to constrain cloud occurrence, height, and amount is demonstrated across all cloud types for many geophysical conditions. In particular, skill is demonstrated for thin Cirrus, as well as some Cumulus and Stratocumulus, cloud types infrared sounders typically struggle to quantify. Furthermore, some improvements in the AIRS Version 5 operational retrieval algorithm are demonstrated. However, limitations in AIRS cloud retrievals are also revealed, including the existence of spurious Cirrus near the tropopause and low cloud layers within Cumulonimbus and Nimbostratus clouds. Likely causes of spurious clouds are identified and the potential for further improvement is discussed

Prayer, Sacrifice, and Service: Themes in the Mormon Folk Narrative Tradition

The purpose of this study was to increase understanding of the Mormon folk group. Specifically, I aimed to analyze the Mormon folk narratives that center on three core values of Mormonism: prayer, sacrifice, and service. This project was an introductory approach, pointing the field of Mormon folk studies toward the study of these three narrative types. As these themes are central to Mormonism, my purpose was to offer more insight and understanding about Latter-day Saints. Looking at these stories, I examined the ways in which Latter-day Saints believe and practice the doctrinal principles that undergird these themes. Furthermore, I discussed the manner in which and the purposes for which Latter-day Saints share these narratives. I analyzed each of the three narrative types in terms of their history, context, structure and patterns, performance qualities and functions, and meaning. This study examined narratives that I collected from various places in Utah. The stories that I collected through interviews formed the foundation of my study. Additionally, I obtained stories by observing storytelling events and conversing interpersonally and in small groups with Latter-day Saints. In order to obtain a larger sampling, I collected some stories from LDS published works. I ended up compiling at least thirty stories for each narrative type. The results of the study included a greater understanding of how prayer, sacrifice, and service operate in Latter-day Saint life. Answered-prayer narratives were found to be a critical aspect of Mormon supernatural belief, as Latter-day Saints seek to involve God in everyday life. Narratives of sacrifice revealed the various ways in which Mormons seek to give up valued activities and interests in order to draw closer to God. Furthermore, service narratives exposed how Latter-day Saints commit themselves to service upon joining the Church and subsequently participate in a multitude of various service opportunities. My analysis of these three narrative types demonstrated essential aspects of what it means to be Mormon

Improving spatial predictability of petroleum resources within the Central Tertiary Basin, Spitsbergen: a geochemical and petrographic study of coals from the eastern and western coalfields

Central Tertiary Basin (CTB) coals from a variety of palaeogeographic conditions within the Longyear and Verkhnij seams, were sampled to assess the relationship between the petroleum present, the remaining generation potential and coal geochemistry in order to improve the spatial predictability of petroleum resources within the basin. Vitrinite reflectance (VR) values from the CTB coals have been shown to be suppressed (Marshall et al., 2015a). This study attempts to quantify and correct for this suppression effect by applying the Lo (1993) method (LoVR), which uses Hydrogen Index (HI) values to modify VR data, and the coal Rank(Sr) scale of Suggate (2000, 2002), a technique not affected by suppression. In addition, the oil generation and expulsion thresholds for the CTB coals were investigated

Electron-Impact Ionization of Be-like C III, N IV, and O V

We present recent measurements of absolute electron-impact ionization cross sections for Be-like C III, N IV, and O V forming Li-like C IV, N V, and O VI. The measurements were taken using the crossed-beams apparatus at Oak Ridge National Laboratory. A gas cell beam attenuation method was used to independently measure the metastable fractions present in the ion beams. The measured ionization cross sections were compared with calculations using the R-matrix with pseudostates and distorted-wave theoretical methods. Best agreement is found with the R-matrix with pseudostates cross sections results that account for the metastable fractions inferred from the gas attenuation measurements. We present a set of recommended rate coefficients for electron-impact single ionization from the ground state and metastable term of each ion

The Effect of Bonding on the Fragmentation of Small Systems

Recent dissociative recombination (DR) experiments have reported that the observed reaction products depend on the structure, bonding, and charge centre of the molecular ion. For examples, the dominant product channel observed in the DR of D5(+)(2), N2O2(+)(1), and D5O2(+)(3) suggests that the former two ions have the form D3(+) D2, and NO(+) NO(1), respectively, whilst the latter is known to have the form D2O D(+) D2O (3). Here we compare and contrast these observations by investigating the DR of one of the simplest such systems, Li(+) H2. This system, a weakly bound cluster with the charge centre located on the lithium atom, will provide us with an excellent opportunity for investigating the role played by the type of bonds and charge centre in the DR process

Strong suppression of Coulomb corrections to the cross section of e+e- pair production in ultrarelativistic nuclear collisions

The Coulomb corrections to the cross section of $e^+e^-$ pair production in ultrarelativistic nuclear collisions are calculated in the next-to-leading approximation with respect to the parameter $L=\ln \gamma_A\gamma_B$ ($\gamma_{A,B}$ are the Lorentz factors of colliding nuclei). We found considerable reduction of the Coulomb corrections even for large $\gamma_A\gamma_B$ due to the suppression of the production of $e^+e^-$ pair with the total energy of the order of a few electron masses in the rest frame of one of the nuclei. Our result explains why the deviation from the Born result were not observed in the experiment at SPS.Comment: 4 pages, RevTe

The discovery of ash dieback in the UK: the making of a focusing event

Why did the identification of ‘Ash Dieback’ (Chalara Fraxinea) in 2012 in the UK catch the national media, public and political zeitgeist, and lead to policy changes, in a way that no other contemporary tree pest or pathogen outbreak has?The identification of Ash Dieback in the UK is conceptualised as a successful ‘focusing event’ and the ways in which it was socially constructed by the media, stakeholders and the government are analysed. National newspaper coverage contributed to the way that the disease was understood and was significant in driving the political response. Ash Dieback’s focal power derived from the perceived scale and nature of its impact; the initial attribution of blame on government; the ‘war-like’ response from the government; and Ash’s status as a threatened ‘native’ tree. The Ash Dieback focusing event has increased the salience of plant health issues amongst policymakers, the public and conservation organisations in the UK