Fast Mesh Refinement in Pseudospectral Optimal Control

Mesh refinement in pseudospectral (PS) optimal control is embarrassingly easy --- simply increase the order $N$ of the Lagrange interpolating polynomial and the mathematics of convergence automates the distribution of the grid points. Unfortunately, as $N$ increases, the condition number of the resulting linear algebra increases as $N^2$; hence, spectral efficiency and accuracy are lost in practice. In this paper, we advance Birkhoff interpolation concepts over an arbitrary grid to generate well-conditioned PS optimal control discretizations. We show that the condition number increases only as $\sqrt{N}$ in general, but is independent of $N$ for the special case of one of the boundary points being fixed. Hence, spectral accuracy and efficiency are maintained as $N$ increases. The effectiveness of the resulting fast mesh refinement strategy is demonstrated by using \underline{polynomials of over a thousandth order} to solve a low-thrust, long-duration orbit transfer problem.Comment: 27 pages, 12 figures, JGCD April 201

X-ray Reflection from Inhomogeneous Accretion Disks: II. Emission Line Variability and Implications for Reverberation Mapping

One of the principal scientific objectives of the upcoming Constellation-X mission is to attempt to map the inner regions of accretion disks around black holes in Seyfert galaxies by reverberation mapping of the Fe K fluorescence line. This area of the disk is likely radiation pressure dominated and subject to various dynamical instabilities. Here, we show that density inhomogeneities in the disk atmosphere resulting from the photon bubble instability (PBI) can cause rapid changes in the X-ray reflection features, even when the illuminating flux is constant. Using a simulation of the development of the PBI, we find that, for the disk parameters chosen, the Fe K and O VIII Ly\alpha lines vary on timescales as short as a few hundredths of an orbital time. In response to the changes in accretion disk structure, the Fe K equivalent width (EW) shows variations as large as ~100 eV. The magnitude and direction (positive or negative) of the changes depends on the ionization state of the atmosphere. The largest changes are found when the disk is moderately ionized. The O VIII EW varies by tens of eV, as well as exhibiting plenty of rapid, low-amplitude changes. This effect provides a natural explanation for some observed instances of short timescale Fe K variability which was uncorrelated with the continuum (e.g., Mrk 841). New predictions for Fe K reverberation mapping should be made which include the effects of this accretion disk driven line variability and a variable ionization state. Reflection spectra averaged over the evolution of the instability are well fit by constant density models in the 2-10 keV region.Comment: 20 pages, 3 figures. Accepted by Ap

Oxygen Isotopic Imaging of Refractory Inclusions from the Miller Range (MIL) 090019 CO3 Chondrite: A Perovskite Perspective

Calcium-Aluminum-rich Inclusions (CAIs) in primitive meteorites are the first solids to condense in the Solar System. The oxygen isotopic compositions recorded in various mineral components of CAIs provide clues about their origins and post-formation histories, recording processes such as condensation, melting, nebular alteration, and fluidrock reactions on the parent body. MIL 090019 is similar to some rare carbonaceous chondrites such as Acfer 094, DOM 08004/6 and ALH 77303 that contain high abundances of a variety of refractory inclusions. This provides an opportunity to study the oxygen isotopic record of different types of refractory inclusions within the same meteorite. We analyzed CAIs specifically targeting primary minerals that are direct nebular condensates, such as corundum and perovskite, with the goal of gaining insights into the O isotopic composition of the nebular gas(es) from which these CAIs condensed. As MIL 090019 is a classified as CO3.1, it shows some signs of thermal metamorphism, compared to the more primitive CO3 meteorites (e.g., DOM 08004/06). A second goal of this study is to search for evidence of nebular processes in phases such as perovskite and melilite that are susceptible to parent body alteration to varying degrees. We analyzed the oxygen isotopic compositions of various CAIs from the MIL 090019 CO3 carbonaceous chondrite by ion imaging using the NanoSIMS 50L (Nano Secondary Ion Mass Spectrometer) at JSC following methods described in. An advantage of ion imaging over traditional spot analyses is that it provides spatial context to the oxygen isotopic data. This work builds on previously reported oxygen isotopic composition of two other CAIs (CAI-44 and CAI-E2) from the same meteorite thin section

On the oscillation of species

We describe a new class of BPS objects called magnetubes: their supersymmetry is determined by their magnetic charges, while their electric charges can oscillate freely between different species. We show how to incorporate these objects into microstate geometries and create BPS solutions in which the charge densities rotate through different U(1) species as one moves around a circle within the microstate geometry. Our solutions have the same “time-like” supersymmetry as five-dimensional, three-charge black holes but, in various parts of the solution, the supersymmetry takes the “null” form that is normally associated with magnetic charges. It is this property that enables the species oscillation of magnetubes to be compatible with supersymmetry. We give an example in which the species oscillate non-trivially around a circle within a microstate geometry, and yet the energy-momentum tensor and metric are completely independent of this circle: only the amplitude of the oscillation influences the metric

Ultraluminous X-ray Sources Powered by Radiatively Efficient Two-Phased Super-Eddington Accretion onto Stellar Mass Black holes

The radiation spectra of many of the brightest ultraluminous X-ray sources (ULXs) are dominated by a hard power law component, likely powered by a hot, optically thin corona that Comptonizes soft seed photons emitted from a cool, optically thick black hole accretion disk. Before its dissipation and subsequent conversion into coronal photon power, the randomized gravitational binding energy responsible for powering ULX phenomena must separate from the mass of its origin by a means other than, and quicker than, electron scattering-mediated radiative diffusion. Therefore, the release of accretion power in ULXs is not necessarily subject to Eddington-limited photon trapping, as long as it occurs in a corona. Motivated by these basic considerations, we present a model of ULXs powered by geometrically thin accretion onto stellar mass black holes. We argue that the radiative efficiency of the flow remains high if the corona is magnetized or optically thin and the majority of the accretion power escapes in the form of radiation rather than an outflow. Within the context of the current black hole X-ray binary paradigm, our ULX model may be viewed as an extension of the very high state observed in Galactic sources. (abridged)Comment: 11 page

Charge-Focusing Readout of Time Projection Chambers

Time projection chambers (TPCs) have found a wide range of applications in particle physics, nuclear physics, and homeland security. For TPCs with high-resolution readout, the readout electronics often dominate the price of the final detector. We have developed a novel method which could be used to build large-scale detectors while limiting the necessary readout area. By focusing the drift charge with static electric fields, we would allow a small area of electronics to be sensitive to particle detection for a much larger detector volume. The resulting cost reduction could be important in areas of research which demand large-scale detectors, including dark matter searches and detection of special nuclear material. We present simulations made using the software package Garfield of a focusing structure to be used with a prototype TPC with pixel readout. This design should enable significant focusing while retaining directional sensitivity to incoming particles. We also present first experimental results and compare them with simulation.Comment: 5 pages, 17 figures, Presented at IEEE Nuclear Science Symposium 201

Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei. III. Integrated Spectra for Hydrogen-Helium Disks

We have constructed a grid of non-LTE disk models for a wide range of black hole mass and mass accretion rate, for several values of viscosity parameter alpha, and for two extreme values of the black hole spin: the maximum-rotation Kerr black hole, and the Schwarzschild (non-rotating) black hole. Our procedure calculates self-consistently the vertical structure of all disk annuli together with the radiation field, without any approximations imposed on the optical thickness of the disk, and without any ad hoc approximations to the behavior of the radiation intensity. The total spectrum of a disk is computed by summing the spectra of the individual annuli, taking into account the general relativistic transfer function. The grid covers nine values of the black hole mass between M = 1/8 and 32 billion solar masses with a two-fold increase of mass for each subsequent value; and eleven values of the mass accretion rate, each a power of 2 times 1 solar mass/year. The highest value of the accretion rate corresponds to 0.3 Eddington. We show the vertical structure of individual annuli within the set of accretion disk models, along with their local emergent flux, and discuss the internal physical self-consistency of the models. We then present the full disk-integrated spectra, and discuss a number of observationally interesting properties of the models, such as optical/ultraviolet colors, the behavior of the hydrogen Lyman limit region, polarization, and number of ionizing photons. Our calculations are far from definitive in terms of the input physics, but generally we find that our models exhibit rather red optical/UV colors. Flux discontinuities in the region of the hydrogen Lyman limit are only present in cool, low luminosity models, while hotter models exhibit blueshifted changes in spectral slope.Comment: 20 pages, 31 figures, ApJ in press, spectral models are available for downloading at http://www.physics.ucsb.edu/~blaes/habk

Predicting rice phenotypes with meta and multi-target learning

The features in some machine learning datasets can naturally be divided into groups. This is the case with genomic data, where features can be grouped by chromosome. In many applications it is common for these groupings to be ignored, as interactions may exist between features belonging to different groups. However, including a group that does not influence a response introduces noise when fitting a model, leading to suboptimal predictive accuracy. Here we present two general frameworks for the generation and combination of meta-features when feature groupings are present. Furthermore, we make comparisons to multi-target learning, given that one is typically interested in predicting multiple phenotypes. We evaluated the frameworks and multi-target learning approaches on a genomic rice dataset where the regression task is to predict plant phenotype. Our results demonstrate that there are use cases for both the meta and multi-target approaches, given that overall, they significantly outperform the base case

Kajian Toksisitas dari Tubuh Buah Ganoderma Lucidum dengan Metode Brine Shrimp Lethality Test (Bst)

Ganoderma lucidum is polyporus fungi from Basidiomycetes which can be used as traditional medicines. Toxicity test with Brine Shrimp Lethality Test (BST) method using Artemia salina was conducted to find out toxic effect of G.lucidum. An extract would have toxic effect if the LC50 < 1000 µg/ml. The aims of this experiment were to know about the toxicity level from G.lucidum with Brine Shrimp Lethality Test (BST) method and determined the concentration of fruiting body extract of G.lucidum which had the best toxicity effect in LC50. There were two extraction methods used in this experiment, first one stage extraction and then multilevel extraction with hexane, ethyl acetate, and ethanol. Each solvent was made in 1000 ppm, 500 ppm, 250 ppm, and 125 ppm. This process was repeated for three times. This experiment used G.lucidum extract which was tested to A.salina and secunder compound metabolit test from the most toxic G. lucidum was done with phytochemical analysis. The result indicated that fruiting body extract from G.lucidum could kill A.salina because all extract was positively contained alkaloid and terpenoid but negatively contained flavonoid. Fruiting body extract from G.lucidum which had lowest LC50 wass ethyl asetat extract with one stage extraction in concentration 53,70 ppm and highest LC50 was ethanol extract with multilevel extraction in concentration 501,18 ppm