28,964 research outputs found
Quasi-molecular lines in Lyman wings of cool DA white dwarfs; Application to FUSE observations of G231-40
We present new theoretical calculations of the total line profiles of Lyman
alpha and Lyman beta which include perturbations by both neutral hydrogen AND
protons and all possible quasi-molecular states of H_2 and H_2^+. They are used
to improve theoretical modeling of synthetic spectra for cool DA white dwarfs.
We compare them with FUSE observation of G231-40. The appearance of the line
wings between Lyman alpha and Lyman beta is shown to be sensitive to the
relative abundance of hydrogen ions and neutral atoms, and thereby to provide a
temperature diagnostic for stellar atmospheres and laboratory plasmas.Comment: 6 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
A high resolution spectral atlas of brown dwarfs
We present a UVES/VLT high resolution atlas of three L dwarfs and one T dwarf
system, spectral classes at which most of the objects are brown dwarfs. Our
atlas covers the optical region from H up to the near infrared at 1
m. We present spectral details of ultra-cool atmospheres at very high
resolution () and compare the spectra to model calculations. Our
comparison shows that molecular features from VO and CaH, and atomic features
from Cs and Rb are reasonably well fit by current models. On the other hand,
features due to TiO, CrH, and water, and atomic Na and K reveal large
discrepancies between model calculations and our observations.Comment: 17 pages, 11 figures, accepted by A&A, reduced figure quality for
arXi
The Origins and Early History of the Steamer Albatross, 1880–18
Spencer Fullerton Baird (Fig. 1), a noted systematic zoologist and builder of scientific institutions in 19th century America, persuaded the U.S. Congress to establish the United States Commission of Fish and Fisheries1 in March 1871. At that time, Baird was Assistant Secretary of the Smithsonian Institution. Following the death of Joseph Henry in 1878, he became head of the institution, a position he held until his own demise in 1887. In addition to his many duties as a Smithsonian official, including his prominent role in developing the Smithsonian’s Federally funded National Museum as the repository for governmental scientific collections, Baird directed the Fish Commission from 1871 until 1887.
The Fish Commission’s original mission was to determine the reasons and remedies for the apparent decline of American fisheries off southern New England as well as other parts of the United States. In 1872, Congress further directed the Commission to begin a large fish hatching program aimed at increasing the supply of American food
The angular resolution of the Pierre Auger Observatory
We discuss the angular resolution obtained for events registered with the
surface detector alone and for hybrid events, i.e., those observed
simultaneously by both the surface and fluorescence detectors. The angular
accuracy of the surface detector is directly extracted from the data itself and
on an event by event basis, and is given as a function of the number of
stations triggered by the event and of the zenith angle of the shower. We
compare the angular resolution of the surface detector obtained from hybrid
events with the one obtained from the surface detector alone.Comment: 6 pages, 8 figures. Presented at CRIS 2008, Malfa, Ital
Creating spaces for pedagogy : research as learning
As teacher-educators, the authors designed and implemented a small study that mapped teacher-education students\u27 understandings of their own identities and how they made sense of ethnicity and class differences among their secondary students while on teaching rounds. While the authors did not set out to \u27teach\u27 their research participants, it was during the analysis of data from the research project, that they began to realise the potential of research to create opportunities for learning. In this paper the authors speculate on the \u27conditions\u27 of knowledge production and suggest that the dialogic nature of interviews and focus group discussions can offer pedagogical spaces for learning. Research designs that incorporate opportunities for participants to re-tell narratives over periods of time, may position participants as experts in knowledge production and may reposition them and researchers in more equitable power relations. The authors present an example of one participant\u27s narrative together with their interpretations to explore how research potentially offers \u27evidence\u27 of learning. While this is tentative only, the authors suggest there is a need to create spaces for pedagogy in the design and execution of educational research.<br /
Euro-productivity and euro-jobs since the 1960s: which institutions mattered?
How have labor market institutions and welfare-state transfers affected jobs and productivity in Europe? Many studies have tackled this question, with mixed results. This paper proposes an eclectic approach and gives a clearer answer to the issue. Orthodox criticisms of European government institutions are right in some cases and wrong in others. Labor-market policies such as employment protection laws have become more costly since 1980 through their human-capital cost of protecting senior male workers at the expense of women and youth. Product-market regulations may have reduced GDP, though the evidence is less robustProductivity, Employment protection legislation, unemployment benefits, social spending, welfare state
Numerical simulations of surface convection in a late M-dwarf
Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD)
simulations of time-dependent compressible convection, we have studied the
dynamics and thermal structure of the convective surface layers of a
prototypical late-type M-dwarf (Teff~2800K log(g)=5.0, solar chemical
composition). The RHD models predict stellar granulation qualitatively similar
to the familiar solar pattern. Quantitatively, the granular cells show a
convective turn-over time scale of ~100s, and a horizontal scale of 80km; the
relative intensity contrast of the granular pattern amounts to 1.1%, and
root-mean-square vertical velocities reach 240m/s at maximum. Deviations from
radiative equilibrium in the higher, formally convectively stable atmospheric
layers are found to be insignificant allowing a reliable modeling of the
atmosphere with 1D standard model atmospheres. A mixing-length parameter of
alpha=2.1 provides the best representation of the average thermal structure of
the RHD model atmosphere while alternative values are found when fitting the
asymptotic entropy encountered in deeper layers of the stellar envelope
alpha=1.5, or when matching the vertical velocity field alpha=3.5. The close
correspondence between RHD and standard model atmospheres implies that
presently existing discrepancies between observed and predicted stellar colors
in the M-dwarf regime cannot be traced back to an inadequate treatment of
convection in the 1D standard models. The RHD models predict a modest extension
of the convectively mixed region beyond the formal Schwarzschild stability
boundary which provides hints for the distribution of dust grains in cooler
(brown dwarf) atmospheres.Comment: 19 pages, 16 figures, accepted for publication in A&
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