Ascent from the lunar surface

Ascent from lunar surface problem with solution by variational calculu

The energy partitioning of non-thermal particles in a plasma: or the Coulomb logarithm revisited

The charged particle stopping power in a highly ionized and weakly to moderately coupled plasma has been calculated to leading and next-to-leading order by Brown, Preston, and Singleton (BPS). After reviewing the main ideas behind this calculation, we use a Fokker-Planck equation derived by BPS to compute the electron-ion energy partitioning of a charged particle traversing a plasma. The motivation for this application is ignition for inertial confinement fusion -- more energy delivered to the ions means a better chance of ignition, and conversely. It is therefore important to calculate the fractional energy loss to electrons and ions as accurately as possible, as this could have implications for the Laser Megajoule (LMJ) facility in France and the National Ignition Facility (NIF) in the United States. The traditional method by which one calculates the electron-ion energy splitting of a charged particle traversing a plasma involves integrating the stopping power dE/dx. However, as the charged particle slows down and becomes thermalized into the background plasma, this method of calculating the electron-ion energy splitting breaks down. As a result, the method suffers a systematic error of order T/E0, where T is the plasma temperature and E0 is the initial energy of the charged particle. In the case of DT fusion, for example, this can lead to uncertainties as high as 10% or so. The formalism presented here is designed to account for the thermalization process, and in contrast, it provides results that are near-exact.Comment: 10 pages, 3 figures, invited talk at the 35th European Physical Society meeting on plasma physic

Analysis of dynamic stall using unsteady boundary-layer theory

The unsteady turbulent boundary layer and potential flow about a pitching airfoil are analyzed using numerical methods to determine the effect of pitch rate on the delay in forward movement of the rear flow reversal point. An explicit finite difference scheme is used to integrate the unsteady boundary layer equations, which are coupled at each instant of time to a fully unsteady and nonlinear potential flow analysis. A substantial delay in forward movement of the reversal point is demonstrated with increasing pitch rate, and it is shown that the delay results partly from the alleviation of the gradients in the potential flow, and partly from the effects of unsteadiness in the boundary layer itself. The predicted delay in flow-reversal onset, and its variation with pitch rate, are shown to be in reasonable agreement with experimental data relating to the delay in dynamic stall. From the comparisons it can be concluded (a) that the effects of time-dependence are sufficient to explain the failure of the boundary layer to separate during the dynamic overshoot, and (b) that there may be some link between forward movement of the reversal point and dynamic stall

Phantom energy from graded algebras

We construct a model of phantom energy using the graded Lie algebra SU(2/1). The negative kinetic energy of the phantom field emerges naturally from the graded Lie algebra, resulting in an equation of state with w<-1. The model also contains ordinary scalar fields and anti-commuting (Grassmann) vector fields which can be taken as two component dark matter. A potential term is generated for both the phantom fields and the ordinary scalar fields via a postulated condensate of the Grassmann vector fields. Since the phantom energy and dark matter arise from the same Lagrangian the phantom energy and dark matter of this model are coupled via the Grassman vector fields. In the model presented here phantom energy and dark matter come from a gauge principle rather than being introduced in an ad hoc manner.Comment: 8 pages no figures; references added and discussion on condensate of vector grassman fields added. To be published MPL

The Stac Fada “impact ejecta” layer: not what it seems

The Stac Fada Member (SFM) forms part of the Stoer Group of the Torridonian of NW Scotland. The SFM is unique in the Torridonian, being characterized by the presence of greenish altered glass clasts. Its origin has been debated for decades with several hypotheses being proposed but all invoking some connection with volcanic activity in the region. More recently, Amor et al. suggested that the SFM represents “a chord section through the continuous ejecta blanket surrounding an impact crater”. Here, we confirm the presence of shocked material within the SFM and then discuss its origin

Periodic Instantons in SU(2) Yang-Mills-Higgs Theory

The properties of periodic instanton solutions of the classical SU(2) gauge theory with a Higgs doublet field are described analytically at low energies, and found numerically for all energies up to and beyond the sphaleron energy. Interesting new classes of bifurcating complex periodic instanton solutions to the Yang-Mills-Higgs equations are described.Comment: 11 pages, 3 figures (in 5 included eps files), ReVTeX (minor typos corrected and reference added

Quantum Oscillations in the Underdoped Cuprate YBa2Cu4O8

We report the observation of quantum oscillations in the underdoped cuprate superconductor YBa2Cu4O8 using a tunnel-diode oscillator technique in pulsed magnetic fields up to 85T. There is a clear signal, periodic in inverse field, with frequency 660+/-15T and possible evidence for the presence of two components of slightly different frequency. The quasiparticle mass is m*=3.0+/-0.3m_e. In conjunction with the results of Doiron-Leyraud et al. for YBa2Cu3O6.5, the present measurements suggest that Fermi surface pockets are a general feature of underdoped copper oxide planes and provide information about the doping dependence of the Fermi surface.Comment: Contains revisions addressing referees' comments including a different Fig 1b. 4 pages, 4 figure

How much effort is required to accurately describe the complex ecology of a rodent‐borne viral disease?

We use data collected on 18, 1-ha live trapping grids monitored from 1994 through 2005 and on five of those grids through 2013 in the mesic northwestern United States to illustrate the complexity of the deer mouse (Peromyscus maniculatus)/Sin Nombre virus (SNV) host-pathogen system. Important factors necessary to understand zoonotic disease ecology include those associated with distribution and population dynamics of reservoir species as well as infection dynamics. Results are based on more than 851,000 trap nights, 16,608 individual deer mice and 10,572 collected blood samples. Deer mice were distributed throughout every habitat we sampled and were present during every sampling period in all habitats except high altitude habitats over 1900 m. Abundance varied greatly among locations with peak numbers occurring mostly during fall. However, peak rodent abundance occurred during fall, winter and spring during various years on three grids trapped 12 months/yr. Prevalence of antibodies to SNV averaged 3.9% to 22.1% but no grids had mice with antibodies during every month. The maximum period without antibody-positive mice ranged from 1 to 52 months, or even more at high altitude grids where deer mice were not always present. Months without antibody-positive mice were more prevalent during fall than spring. Population fluctuations were not synchronous over broad geographic areas and antibody prevalences were not well spatially consistent, differing greatly over short distances. We observed an apparently negative, but nonstatistically significant relationship between average antibody prevalence and average deer mouse population abundance and a statistically significant positive relationship between the average number of antibody positive mice and average population abundance. We present data from which potential researchers can estimate the effort required to adequately describe the ecology of a rodentborne viral system. We address different factors affecting population dynamics and hantavirus antibody prevalence and discuss the path to understanding a complex rodent-borne disease system as well as the obstacles in that path.Fil: Douglass, Richard J.. University of Montana; Estados UnidosFil: Vadell, María Victoria. Universidad Nacional de San Martín. Instituto de Investigaciones e Ingeniería Ambiental. Laboratorio de Ecología de Enfermedades Transmitidas por Vectores; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Uncovering predictability in the evolution of the WTI oil futures curve

Accurately forecasting the price of oil, the world's most actively traded commodity, is of great importance to both academics and practitioners. We contribute by proposing a functional time series based method to model and forecast oil futures. Our approach boasts a number of theoretical and practical advantages including effectively exploiting underlying process dynamics missed by classical discrete approaches. We evaluate the finite-sample performance against established benchmarks using a model confidence set test. A realistic out-of-sample exercise provides strong support for the adoption of our approach with it residing in the superior set of models in all considered instances.Comment: 28 pages, 4 figures, to appear in European Financial Managemen