13,204 research outputs found
The ISO-LWS map of the Serpens cloud core. II. The line spectra
We present spectrophotometric ISO imaging with the LWS and the CAM-CVF of the
Serpens molecular cloud core. The LWS map is centred on the far infrared and
submillimetre source SMM1 and its size is 8' x 8'. The fine structure line
emission in [OI] and [CII] is extended and can be successfully modelled to
originate in a PDR with G_0 = 15 and n(H2) about 10^4 - 10^5 cm^-3. Extended
emission is also observed in the rotational line emission of H2O and high-J CO.
However, lack of sufficient angular resolution prevents us from excluding the
possibility that the emssion regions of these lines are point like, which could
be linked to the embedded objects SMM9 and SMM4. Toward the Class0 source SMM1,
the LWS observations reveal, in addition to fine structure line emission, a
rich spectrum of molecular lines. The sub-thermally excited and optically thick
CO, H2O and OH lines are tracing an about 10^3 AU source with temperatures
higher than 300 K and densities above 10^6 cm^-3. We show that geometry is of
concern for the correct interpretation of the data and based on 2D-radiative
transfer modelling of the disk/torus around SMM1, which successfully reproduces
the entire observed SED and the observed line profiles of CO isotopomers, we
can exclude the disk to be the source of the LWS-molecular line emission. The
CAM-CVF permits us to see a region of rotational H2 emission. This H2 gas has a
temperature of 10^3 K, which suggests that the heating of the gas is achieved
through relatively slow shocks. Although we are not able to establish any firm
conclusion regarding the detailed nature of the shock waves, our observations
of the molecular line emission from SMM1 can be explainable in terms of an
admixture of J-shocks and of C-shocks.Comment: 20 pages, 20 figures, accepted for publication in A&
Visualization, Exploration and Data Analysis of Complex Astrophysical Data
In this paper we show how advanced visualization tools can help the
researcher in investigating and extracting information from data. The focus is
on VisIVO, a novel open source graphics application, which blends high
performance multidimensional visualization techniques and up-to-date
technologies to cooperate with other applications and to access remote,
distributed data archives. VisIVO supports the standards defined by the
International Virtual Observatory Alliance in order to make it interoperable
with VO data repositories. The paper describes the basic technical details and
features of the software and it dedicates a large section to show how VisIVO
can be used in several scientific cases.Comment: 32 pages, 15 figures, accepted by PAS
Evaluation methods among corporate travel managers
This study examined whether corporate travel planners performed any kind of evaluation among their clients and in that case what that evaluation revealed about the different air lines\u27 performance. A questionnaire was sent out to 100 members of National Business Travel Association (NBTA) all over the U.S. In this questionnaire the respondents were asked to answer 10 questions about if and how the evaluated the performance of the airlines. In the survey, 25% of the respondents said that they did not perform any evaluation at all. The most commonly used evaluation method was to hand-out questionnaires which was used by 37.5%. Focus groups were used by 11% of the respondents as an evaluation method. When asked why they did not perform focus groups 40% said it was too time consuming. None of the respondents indicated that it was too expensive or that they did not have the knowledge. When conducting focus groups the most commonly used method was to pick out participators from a frequent flier list provided by the airlines. The top issued brought up in their evaluation whether they used focus groups or any other kind of evaluation method, was arrival time of the airlines. The highest rated U. S carrier was USAir followed by United and the highest rated transatlantic carrier was British Airways followed by SAS
Progenitors of Long Gamma-ray Bursts
Pinpointing the progenitors of long duration gamma-ray bursts (LGRBs) remains
an extremely important question, although it is now clear that at least a
fraction of LGRBs originate in the core collapse of massive stars in type Ic
supernovae, the pathways to the production of these stars, and their initial
masses, remain uncertain. Rotation is thought to be vital in the creation of
LGRBs, and it is likely that black hole creation is also necessary. We suggest
that these two constraints can be met if the GRB progenitors are very massive
stars (>20 solar masses) and are formed in tight binary systems. Using simple
models we compare the predictions of this scenario with observations and find
that the location of GRBs on their host galaxies are suggestive of
main-sequence masses in excess of 20 solar masses, while 50% of the known
compact binary systems may have been sufficiently close to have had the
necessary rotation rates for GRB creation. Thus, massive stars in compact
binaries are a likely channel for at least some fraction of LGRBs.Comment: To appear in "Gamma-ray bursts: Prospects for GLAST", AIP Conference
proceedings 906, Editors M. Axelsson and F Ryd
Qubits from Number States and Bell Inequalities for Number Measurements
Bell inequalities for number measurements are derived via the observation
that the bits of the number indexing a number state are proper qubits.
Violations of these inequalities are obtained from the output state of the
nondegenerate optical parametric amplifier.Comment: revtex4, 7 pages, v2: results identical but extended presentation,
v3: published versio
An adaptive-binning method for generating constant-uncertainty/constant-significance light curves with Fermi-LAT data
We present a method enabling the creation of
constant-uncertainty/constant-significance light curves with the data of the
Fermi-Large Area Telescope (LAT). The adaptive-binning method enables more
information to be encapsulated within the light curve than with the
fixed-binning method. Although primarily developed for blazar studies, it can
be applied to any sources. This method allows the starting and ending times of
each interval to be calculated in a simple and quick way during a first step.
The reported mean flux and spectral index (assuming the spectrum is a power-law
distribution) in the interval are calculated via the standard LAT analysis
during a second step. The absence of major caveats associated with this method
has been established by means of Monte-Carlo simulations. We present the
performance of this method in determining duty cycles as well as power-density
spectra relative to the traditional fixed-binning method.Comment: 17 pages, 13 figures, 5 tables. Submitted to A&
TFAM forces mtDNA to make a U-turn
The mammalian mitochondrial transcription factor A (TFAM) is encoded in the nucleus and imported into mitochondria, where it functions as an activator of mtDNA transcription and packages mtDNA into DNA-protein aggregates called mitochondrial nucleoids. Two X-ray crystallography studies in this issue reveal that TFAM shapes mtDNA into a sharp U-turn, thereby providing a molecular mechanism for its dual roles in the expression and maintenance of mtDNA.VetenskapsrådetPublishe
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