bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct Comparison of Electron Density Measurements in Laser-Created Plasmas Using Stark Broadening and Satellite Line Intensities
Authors: Alaterre Ph. , Audebert P. , Geindre J.P. , Monier P. , Popovics C. , Gauthier J.C. 
Published: July 2016

Spectral line profiles, broadened mostly by Stark effects from electric fields produced by charge particles, and diélectronic satellite line intensities have recently been used for determining electron densities in the dense region of laser-created plasmas. We present here a direct comparison of electron density measurements in the conduction region of laser created plasmas on a plane target using these two techniques.Experiments were carried at the GRECO laser facility, using the Nd phosphate glass laser at its second harmonic (0.53 μm) and 600 ps pulse length. The laser was focused on a 160 μm focal spot in which was centered a 25 or 50 μm diameter aluminum dot implanted on a carbon substrate. Laser intensities were in the range 1 × 1014−3 × 1014 W/cm2. The ls4p−ls2 He-like transition, the 4p−ls H-like transition and the Ly c satellites were recorded on the same spectrum with a PET flat crystal spectrograph. Spot spectroscopy provided quasi-homogeneity and low reabsorption along the line of sight which was tilted 7° out the target surface. 3 μm resolution along the laser axis was obtained with an imaging knife-edge placed 1 mm apart from the target.
Absorption Spectra of Light Ions in the Extreme Ultraviolet
Authors: Jannitti E. , Nicolosi P. , Pinzhong F. , Tondello G. 
Published: July 2016

We have used the method of two laser produced plasmas (Jannitti et al. 1984a) to measure the absorption spectra of the ions Be++ (Jannitti et al. 1984b), Be+ (Jannitti et al. 1984c) and B+ in the grazing incidence and normal incidence region. Both discrete and continua transitions have been measured and values of the photoionization cross sections are derived.The experimental set up referring to the normal incidence investigation is shown in Fig. 1. A laser beam of 10 J of energy and 15 ns (FWHM) duration is split in two parts and generates two plasmas: one on target T of high atomic number (Cu) used as a background continuum emitting source and a second on target A for producing the absorbing species to be studied. For the latter a sphero-cylindrical lens is used producing a focal spot 100 µm wide and up to 10 mm long. The continuum radiation produced on a target tilted 45° both with respect to the laser beam and to the axis of observation was collected by a toroidal mirror whose radii of curvature, R = 640 mm in the plane of incidence and ρ = 530 mm in the plane perpendicular to the former are such to compensate the astigmatism of the 2 m radius grating.
Theory of Protostellar Objects
Authors: Shu Frank H. 
Published: July 2016

AbstractMany problems in the theory of star formation are amenable to a complementary attack in which the analytical approach is used to reduce the governing equations to a form amenable to efficient numerical solution. This strategy has proven very useful in helping to resolve several astrophysical puzzles which arise because the bulk of star formation today is observed to occur, with relatively low efficiency, in giant molecular cloud complexes. How does a cloud of 105-106M⊙ know how to form stars of mass ~ 1 M⊙? How does the interstellar medium know, to one or two orders of magnitude, that roughly hydrogen atoms of mass mH are needed to yield thermonuclear fusion in a self-gravitating ball of gas? Why have radio astronomers not detected unambiguous evidence for the collapse motions attendant to star formation? Why has a true protostar, the “holy grail” of infrared astronomy, been so hard to find? Why do young stellar objects almost universally exhibit powerful outflows? Why is the geometry for these outflows often bipolar? Why do T Tauri stars have such active chromospheres? In this review we suggest that these puzzles all have a related resolution, in the nature of how gravitational collapse is initiated and terminated in the slowly rotating cores of molecular clouds.
Radiation Hydrodynamics in Solar Flares
Authors: Fisher George H. 
Published: July 2016

AbstractSolar flares are currently understood as the explosive release of energy stored in the form of stressed magnetic fields. In many cases, the released energy seems to take the form of large numbers of electrons accelerated to high energies (the nonthermal electron “thick target” model), or alternatively plasma heated to very high temperatures behind a rapidly moving conduction front (the “thermal” model). The transport of this energy into the remaining portion of the atmosphere results in violent mass motion and strong emission across the electromagnetic spectrum. Radiation processes play a crucial role in determining the ensuing plasma motion.One important phenomenon observed during flares is the appearance in coronal magnetic loops of large amounts of upflowing, soft X-ray emitting plasma at temperatures of 1−2×107[K]. It is believed that this is due to chromospheric evaporation, the process of heating cool (T - 104[K]) chromospheric material beyond its ability to radiate. Detailed calculations of thick target heating show that if nonthermal electrons heat the chromosphere directly, then the evaporation process can result in explosive upward motion of X-ray emitting plasma if the heating rate exceeds a threshold value. In such a case, upflow velocities approach an upper limit of roughly 2.35 csas the heating rate is increased beyond the threshold, where csis the sound speed in the evaporated plasma. This is known as explosive evaporation. If the flare heating rate is less than the threshold, evaporation takes place indirectly through thermal conduction of heat deposited in the corona by the energetic electrons. Upflows in this case are roughly 10 to 20% of the upper limit. Evaporation by thermal model heating always takes place through thermal conduction, and the computed upflow speeds seem to be about 10% to 20% of the upper limit, independent of the energy flux.The pressure increase in the evaporated plasma for either the thick target or thermal model leads to a number of interesting phenomena in the flare chromosphere. The sudden pressure increase initiates a downward moving “chromospheric condensation”, an overdense region which gradually decelerates as it accretes material and propagates into the gravitationally stratified chromosphere. Solutions to an equation of motion for this condensation shows that its motion decays after about one minute of propagation into the chromosphere. When the front of this downflowing region is supersonic relative to the atmosphere ahead of it, a radiating shock will form. If the downflow is rapid enough, the shock strength should be sufficient to excite UV radiation normally associated with the transition region, and furthermore, the radiating shock will be brighter than the transition region. These results lead to a number of observationally testable relationships between the optical and ultraviolet spectra from the condensation and radiating shock.
Physical Processes in Active Galactic Nuclei
Authors: Svensson Roland 
Published: July 2016

AbstractActive galactic nuclei (AGNs) emit continuum radiation evenly spread over up to ten decades in frequency from the radio into the gamma-ray range. Plausible emission mechanisms and their characteristics are reviewed. In the deep potential wells around black holes the mean energy per proton can reach 100 MeV. Part or all of this energy may be channeled to all electrons equally (thermal plasma) or, preferentially, into only a small fraction of the electrons (nonthermal plasma). In the former case thermal Comptonization of soft photons may be the dominant emission mechanism, while in the latter case the synchrotron and the inverse Compton scattering process (synchro-self-Compton) are likely to dominate.When the compactness parameter L (hν≈mc2 )/R. (power L, radius R) exceeds about 1030 ergs cm−1s−1 or L>Lc ≡ 1030R ergs s−1, then electron-positron pair production takes place due to photon-photon interactions causing the source to shroud itself with an electron-positron atmosphere. The efficiency of pair cascades in converting injected energy into electron-positron rest mass can reach levels of about 10% in static pair atmospheres. The emerging radiation is strongly modified by the pair atmosphere causing the spectrum to soften and to have characteristic breaks.For emission coming from a region near the Schwarzschild radius, L>10-3LEdd is sufficient to cause prolific pair production. Radiation pressure then drives a mildly relativistic pair wind with Compton drag limiting the Lorentz factor to be less then 10. The pair rest mass power is at most of the order of Lc.Most results so far on static pair atmospheres and pair winds are either qualitative or based on simple analytical models. Needed numerical treatments of both time dependent and steady radiative transfer of both the continuum and the annihilation line radiation in mildly relativistic flows are relevant not only for AGNs but also for gamma ray bursts and galactic black hole sources.
Hydrodynamics Near the Central Engine
Authors: Hawley John F. 
Published: July 2016

AbstractThe “central engine” of quasars and active galactic nuclei Is most likely powered by accretion into a supermassive black hole. A menagerie of steady state accretion flows have been developed, and these are briefly reviewed. Several examples from recent numerical calculations of axisymmetric accretion flows provide disk formation scenarios from which one can calculate plasma densities, and other values of interest for a range of accretion rates and black hole masses. These results can be compared with the well studied, but physically unrealistic case of radial accretion. Although a reasonable conceptual picture of the central engine has been developed, considerable work remains to be done.
Radiation Hydrodynamics: Conference Themes and Unsolved Problems
Authors: Shull J. Michael 
Published: July 2016

This paper will be a short review of the topics covered at this conference on “Radiation Hydrodynamics in Stars and Compact Objects.” Rather than attempt to cover all the talks and posters, I will describe what I saw as the main themes and then summarize selected topics that provided unsolved questions. Finally, I will try to decide whether we strayed too far from the original purpose of the meeting. Or, put as a question: Does Radiation Hydrodynamics play a major role in solving a wide range of astrophysical problems?As described in Mihalas’ introductory talk, radiation can affect an astrophysical plasma, flow, or object in several fashions. First, it can influence the kinematics through ionization, dissociation, and other gas-phase processes that depend on chemistry, ionization state, or excitation. But second, it can influence the dynamics of the flow, through deposition of momentum. Examples of the latter are shock waves, accretion disks, novae, supernovae, and hot-star winds. One can, therefore, divide the topics at this meeting into “active” and “passive” classes of radiation hydrodynamic problems (Table 1). The term “active” implies dynamic pressure from the radiation, whereas the term “passive” allows the radiation to affect the state of the gas, particularly its spectral emissivity, without affecting its motion appreciably.
Astronomy Education in Hungary
Authors: Szécsényi-Nagy Gábor 
Published: July 2016

Our educational system, like that of any other country, has grown up to meet the needs of the environment in which it developed. Perhaps its most distinctive feature is its emphasis on education of the masses rather than on education of the intellectuals.The philosophy of the Hungarian educational system is that a democracy depends upon a well-informed electorate, and that therefore each citizen should receive the best education possible. As a result, in our country most children in the same community attend school together from kindergarten through secondary school practically regardless of differences in intellectual ability or in family background.
Interdisciplinary Approaches to Astronomy
Authors: Fraknoi Andrew 
Published: July 2016

To understand the motivation for my talk, you must bear in mind what Don Wentzel discussed so eloquently at the beginning of the colloquium. In the U.S., the vast majority of students taking astronomy classes at the college level are not science majors. Many students coming into the astronomy courses are afraid and distrustful of science and often see science as a very alien endeavor, quite separate from their everyday lives and other studies.For such students, it can sometimes be very reassuring and enlightening to show some interesting connections between astronomy and other (nonscience) fields at a few places in the introductory astronomy course. For example, many students are surprised and excited to see the inspiration that astronomy has provided for music, literature, and art and some of the interesting connections between astronomy and psychology, archaeology, and law.
Astronomy as a Liberal Art
Authors: Dennis Tom R. 
Published: July 2016

Every year in the United States, many thousands of university and college students take a one-semester course in astronomy as part of a “Liberal Arts” curriculum. At many institutions these courses are the raison d’etre for the astronomy program, and at most other institutions they are viewed as an important term in calculating an astronomy department’s contribution.I have often had a sense that what we are doing in these courses is counter-productive to any serious understanding of the goals of liberal arts curriculum. Over the last six or seven years, as I have been participating in my college’s efforts to introduce a year-long, interdisciplinary survey of the humanities into our curriculum, this hunch has been confirmed: in our efforts to fit astronomy into the liberal-arts curriculum, we have ironically been undermining the enterprise.
The Role of Projects in Astronomy Education
Authors: McNally D. 
Published: July 2016

At first sight, there may appear to be a very wide range of project situations that are in use. Students may seem to be doing the equivalent of postgraduate work, or may seem to be working on contract basis, or may even seem to be doing rather long term laboratory exercises, or some mixture of all three. However, there are in essence two major types of project situations — the free-scope project and the set-piece project.The free-scope project attaches importance to the selection of project topics by the student. The student may be told to select a problem from the entire spectrum of problems offered by the science of astronomy, and to get on with it, or there may be guidelines to restrict the choice. Nevertheless, the choice of topic is the prerogative of the student, and it is believed that the effort of making that choice is important in the teaching/learning process. Because of the range of formats for free-scope projects, it is a convenient form to adapt to meet varying local circumstances.
The Edinburgh Astronomy Teaching and Educational Packages
Authors: Brück M.T. , Tritton S.B. 
Published: July 2016

In this paper we describe our experiences with film copies of original astronomical photographs taken with the 1.2-meter U.K. Schmidt Telescope (UKST) in Australia, and used as teaching material in the Department of Astronomy of the University of Edinburgh. Two packages are intended for undergraduate use; the Education Packages are designed as visual aids for colleges, schools, and amateur groups.The original purpose of the telescope (which was commissioned in 1973) was to carry out a Southern Sky Survey to match the Northern Survey done by the Palomar 48” Schmidt Telescope. The telescope has a very wide field — 6.5 × 6.5 degrees, or equivalent to over a hundred and fifty full moons, and the photographs reach objects of 23rd magnitude: they record stars like the Sun to the very edges of the Galaxy and galaxies to a thousand million light years. Each photograph has an area of 356 × 356 mm and records between 100,000 and 1 million stars and galaxies. The survey photographs are the deepest available maps of the sky and are indispensable tools for astronomers in searches for unusual objects, for investigation of the distribution of galaxies and many other tasks. The UKST is equipped with objective prisms that are capable of producing low dispersion spectra of stars and galaxies. A prism of very small angle is placed in front of the aperture of the telescope so that each individual image is drawn out into a tiny spectrum on the photograph. The dispersion is very small, only a few millimeters from the red to the ultraviolet, but the dominant features in the spectra are recognizable and have many applications.
Introductory Astronomy Textbooks in 19th and 20th Century America
Authors: Sperling Norman 
Published: July 2016

A survey of 138 introductory-astronomy textbooks spanning 152 years reveals growing consensus regarding each topic’s proportion, with some clearly gaining space at the expense of others. The tables in the texts cite curious numbers, claim too many significant digits, neglect to note uncertainties, and are frequently inconsistent with, or badly behind, the research of the times. This study investigates apportionment of topics, planet and star data tables, and categorization of nebulae.To probe the student/textbook interaction, I used one copy of each of 40 recent introductory textbooks when teaching astronomy in Fall 1986. Students swapped books each session. Texts’ treatments were surveyed in daily recitation as well as term papers comparing and contrasting them on specific topics. Most books sound much more positive than current data justify. There was lots of confusing phrasing, shoddy proofreading, and careless assembly of data tables. A few books are shamefully erroneous. There are numerous impressive examples of the imperfection and transience of “textbook learning.” The biggest and most pervasive sin was writing in the passive voice “Official Style” of interminable sentences laden with prepositional phrases. Illustrations, while important, are secondary to phrasing. Students need and use chapter summaries, glossaries, and indices. About half prefer paperbacks and half hardbacks. Students rated the books for appropriateness to their needs. The experience may stimulate others to develop controlled experiments to probe the student/textbook interaction.
Popularizing Astronomy at Public Observatories in West Germany
Authors: Neumann Hans L. 
Published: July 2016

Based on the pedagogical ideas of A. Diesterweg, a number of science associations have been founded since about 1880 under the name of URANIA; astronomy has been one of their subjects. In the 1920–1930’s, the works of Bruno H. Bürgel and Robert Henseling initiated the founding of many more local and regional associations and of public observatories all over the country. But most of the currently active associations were founded to answer the sharp increase of general interest that followed the early successes and spectacular results of space science.- Aims of the associations always have been manyfold:- to share a fine hobby with like-minded people;- to participate theoretically or practically in scientific research as far as technical and local circumstances allow;- to offer to the public means and advice for celestial observations, and to share the joy of deep-sky wonders with guests;- to mediate the progress, and the results of astronomical research to the public.
Sydney Observatory Goes Public
Authors: Lomb N.R. , Wilson T. 
Published: July 2016

In 1982, after a 124-year history of research, Sydney Observatory became a branch of a large local museum, the Museum of Applied Arts and Sciences. A four-year, million-dollar project was undertaken to restore the building and its grounds to their nineteenth century appearance. The services needed for a modern museum were also added. One of the larger areas became a modern lecture theater seating up to fifty people, with back projection video, film and slide projectors.Exhibition space within the building is limited to eight rooms of approximately 200 m2 total area. To overcome this lack of space, a proposal has been made for an extension to the rear of the building. An underground 100-seat planetarium is included in the proposal. There is a great need for this as there is no planetarium currently in Sydney.
Marketing for Planetariums
Authors: Feitzinger J.V. 
Published: July 2016

The sales promotion of the planetarium is a marketing problem. Program arrangements must take this into account. Marketing is not exclusively a tool to obtain a maximum profit: marketing methods can control the exchange problems between the public and the nonprofit planetarium. The planetarium produces a service. This service must be distributed to the public. The public must know that the planetarium distributes a special service.The public visits the planetarium during leisure time. (One exception — the school classes — is not considered here.) Therefore one marketing problem of the planetarium is to sell its service as recreational value.The leisure time activities of the public can be divided into 10 categories. These categories contain the basic patterns and needs of the public. The content of the public planetarium performances must try to cover the leisure-time categories. The communication windows of the public can only be reached by simplifying astronomical facts.
Knowledge and Wonder in the Planetarium
Authors: Dunlap J. Lawrence 
Published: July 2016

Planetariums around the world attract millions of adults and children each year to public programs popularizing astronomy and related topics. For many urban school children, the planetarium experience is a unique opportunity to observe and to wonder about the night sky and objects in space. In particular, the planetarium provides children with a needed observational basis for increasing scientific literacy and for understanding astronomical concepts.This paper explores the role of the planetarium in the astronomy education of school children, grades Kindergarten–12, in Tucson, Arizona, over the past 12 years.
The Visiting Lecturers Program at San Marcos University
Authors: Aguilar María Luisa H. 
Published: July 2016

Professors and students of San Marcos University (USM) have found that the Visiting Lecturers Program (VLP) of the IAU has helped to improve the study of astronomy in Peru. The Peruvian people and I are profoundly grateful.The VLP and the International Schools for Young Astronomers (ISYA) advised us, pointing our perspectives and capacity for work in the correct direction. I feel that both the VLP and the ISYA are noble expressions of the universal message of scientific collaboration, and are the voices of the highest altruism of the astronomers who participate in them.With reference to the VLP, the state of astronomy education can be described in three parts: