1,524 research outputs found
L1157: Interaction of the molecular outflow with the Class 0 environment
No full textWe present high angular resolution interferometric
observations
of the dust continuum at
2.7 and 1.3 mm, and of the HC3N () and
C18O () emission around L1157-mm, a Class 0 object that
drives a spectacular molecular outflow. The millimeter dust emission
is clearly resolved into two components, a flattened compact source of
~ AU at 1.3 mm, and mass ~0.1 , plus
an extended envelope of ~3000 AU at 1.3 mm, and mass
~1.1 . The millimeter spectral index varies throughout
the region, with the lower value found toward the compact protostar,
possibly indicating grain growth in the denser regions. A strong
interaction between the molecular outflow and the close protostellar
environment is taking place and affects the structure of the innermost
parts of the envelope. This is shown by the spatial coincidence
between the molecular outflow and the dust (1.3 mm continuum) and
HC3N emission: both tracers show structures associated to the edges
of the outflow lobes. Basically, the global picture sketched for the
Class 0 object L1157-mm by Gueth et al. ([CITE]) is supported. We find
possible evidence of infall, but we do not detect any velocity
gradient indicative of a rotating circumstellar disk
The long-wavelength view of GG Tau A: rocks in the ring world
No full textWe present the first detection of GG Tau A at centimetre wavelengths, made with the Arcminute Microkelvin Imager Large Array at a frequency of 16 GHz (λ = 1.8 cm). The source is detected at >6 σrms with an integrated flux density of S16GHz = 249 ± 45 µJy. We use these new centimetre-wave data, in conjunction with additional measurements compiled from the literature, to investigate the long-wavelength tail of the dust emission from this unusual protoplanetary system. We use an MCMC-based method to determine maximum likelihood parameters for a simple parametric spectral model and consider the opacity and mass of the dust contributing to the microwave emission. We derive a dust mass of Md ~ 0.1 Msun, constrain the dimensions of the emitting region and find that the opacity index at λ > 7 mm is less than unity, implying a contribution to the dust population from grains exceeding ~4 cm in size. We suggest that this indicates coagulation within the GG Tau A system has proceeded to the point where dust grains have grown to the size of small rocks with dimensions of a few centimetres. Considering the relatively young age of the GG Tau association in combination with the low derived disc mass, we suggest that this system may provide a useful test case for rapid core accretion planet formation models
A scaling-relation for disc galaxies: circular-velocity gradient versus central surface brightness
No full textFor disc galaxies, a close relation exists between the distribution of light and the
shape of the rotation curve. We quantify this relation by measuring the inner circular-
velocity gradient dRV (0) for spiral and irregular galaxies with high-quality rotation
curves. We find that dRV (0) correlates with the central surface brightness μ0 over
more than two orders of magnitude in dRV (0) and four orders of magnitudes in μ0.
This is a scaling-relation for disc galaxies. It shows that the central stellar density of a
galaxy closely relates to the inner shape of the potential well, also for low-luminosity
and low-surface-brightness galaxies that are expected to be dominated by dark matter.
Key words: dark matter – galaxies: kinematics and dynamics – galaxies: structure
A Note on Case-Based Optimization with a Non-Degenerate Similarity Function
No full textThe paper applies the ��realistic-ambitious�� rule for adaptation of the aspiration level suggested by Gilboa and Schmeidler (1996) to a situation in which the similarity between the available acts is represented by a non-degenerate function. The paper shows that the optimality result obtained by Gilboa and Schmeidler (1996) in general fails. With a concave similarity function, the best corner act is chosen in the limit. Introducing convex regions into the similarity function improves the limit choice. A sufficiently fine similarity function allows to approximate optimal behavior with an arbitrary degree of precision.
On a Diophantine equation involving powers of Fibonacci numbers
No full textThis paper deals with the diophantine equation F-1(p) + 2F(2)(p )+ . . . + kF(k)(p) = F-n(q), an equation on the weighted power terms of Fibonacci sequence. For the exponents p, q is an element of {1, 2} the problem has already been solved in ad hoc ways using the properties of the summatory identities appear on the left-hand side of the equation. Here we suggest a uniform treatment for arbitrary positive integers p and q which works, in practice, for small values. We obtained all the solutions for p, q <= 10 by testing the new approach
Do Social Networks Inspire Employment? - An Experimental Analysis -
No full textThere is robust field data showing that a frequent and successful way of looking for a job is via the intermediation of friends and relatives. Here we want to test this experimentally. Participants first play a simple public goods game with two interaction partners ('friends'), and share whatever they earn this way with two different sharing partners ('cousins') who have different friends. Thus one's social network contains two 'friends' and two 'cousins'. In the second phase of the experiment participants learn about a job opportunity for themselves and one additional vacancy and decide whom of their network they want to recommend and, if so, in which order. In case of coemployment, both employees compete for a bonus. Will one recommend others for the additional job in spite of this competition, will one prefer 'friends' or 'cousins' and how does this depend on contributions (of 'friends') or shared profits (with 'cousins')? Our findings are partly quite puzzling. Most participants, for instance, recommend quite actively but compete very fiercely for the bonus.
(Sub) Optimality and (Non) Optimal Satisficing in Risky Decision Experiments
No full textA risky choice experiment is based on one-dimensional choice variables and risk neutrality induced via binary lottery incentives. Each participant confronts many parameter constellations with varying optimal payoffs. We assess (sub)optimality, as well as (non)optimal satisficing, partly by eliciting aspirations in addition to choices. Treatments differ in the probability that a binary random event, which are payoff- but not optimal choice–relevant, is experimentally induced and whether participants choose portfolios directly or via satisficing, i.e., by forming aspirations and checking for satisficing before making their choice. By incentivizing aspiration formation, we can test satisficing, and in cases of satisficing, determine whether it is optimal
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