208,711 research outputs found
‘Collective intelligence’ is not necessarily present in virtual groups
When we communicate online, we miss an important element of group intelligence: social sensitivity, write Jordan B. Barlow and Alan R. Denni
Properties of distributions with increasing failure rate
This paper solves the search for interior solutions to optimization problems using stochastic variables. This is done by way of some new properties of distribution functions with increasing failure rates as characterized in Barlow and Proschan (1965). Building upon Lariviere (2006), we show that an objective function of the type R(x) = F(x)+xF(x), where F(x) = 1-F(x), can also admit one interior maximal solution when the distribution function F has an increasing failure rate (IFR).optimization problem; probability distribution; increasing failure rate; objective function
The Real-Time Evolution of Sakurai's Star (V4334 Sgr) and other (V)LTP Objects
We report on the progress of our on-going campaign to monitor the evolution
of the VLTP objects V4334 Sgr and V605 Aql, as well as the suspected (V)LTP
object CK Vul. V4334 Sgr does not show signs of increased ionization compared
to our previous observations in 2004. We obtained the first radio detection of
V605 Aql, indicating a strong increase in radio flux since 1987. We also
present the first radio detection of CK Vul and discuss the expansion of the
material ejected during the 1670 event.Comment: 4 pages, 2 figures in eps format, IAU symp. 234: `Planetary Nebulae
in our Galaxy and Beyond', eds. M. J. Barlow & R. H. Mende
Infrared Imaging of Planetary Nebulae from the Ground Up
New ground-based telescopes and instruments, the return of the NICMOS
instrument on the Hubble Space Telescope (HST), and the recent launch of the
Spitzer Space Telescope have provided new tools that are being utilized in the
study of planetary nebulae. Multiwavelength, high spatial resolution
ground-based and HST imaging have been used to probe the inner regions of young
PNe to determine their structure and evaluate formation mechanisms.
Spitzer/IRAC and MIPS have been used to image more evolved PNe to determine the
spatial distribution of molecular hydrogen, ionized gas, and dust in the
nebulae and halos.Comment: 8 pages, 3 figures, invited review given at IAU Symp. 234, to appear
in "Planetary Nebulae in Our Galaxy and Beyond", eds. M. J. Barlow & R. H.
Mende
Bound person forms in ditransitive clauses revisited.
In a recent article Gensler (2003) has argued that little can be said about the ordering of bound person markers of the T(heme) and R(ecipient) relative to each other or relative to the verb stem apart from the fact that the outer markers are likely to be the result of a second-level cliticization process. We take issue with this claim and document that quite successful predictions with respect to the ordering of the T and R markers can be made on the basis of morphological alignment. Taking as our point of departure the typology of ditransitive alignment outlined in Haspelmath (2004; 2005), we show that the ordering patterns in which the R is placed closer to the verbal stem than the T are favoured in all relevant alignment types apart from the indirective, which exhibits a preference for positioning the T closer to the verbal stem than the R. These preferences for the ordering of the R and T are argued to relate directly to the frequency of use of the relative person forms and thus are seen as constituting yet another piece of evidence for the usage-based model of grammar being developed within the functional-cognitive typological paradigm (cf. e.g. Barlow & Kemmer 2000; Bybee & Hopper 2001; Tomasello 2003)
New accurate measurement of 36ArH+ and 38ArH+ ro-vibrational transitions by high resolution IR absorption spectroscopy
The protonated Argon ion, ArH, has been identified recently in
the Crab Nebula (Barlow et al. 2013) from Herschel spectra. Given the
atmospheric opacity at the frequency of its =1-0 and =2-1 rotational
transitions (617.5 and 1234.6 GHz, respectively), and the current lack of
appropriate space observatories after the recent end of the Herschel mission,
future studies on this molecule will rely on mid-infrared observations. We
report on accurate wavenumber measurements of ArH and
ArH rotation-vibration transitions in the =1-0 band in the
range 4.1-3.7 m (2450-2715 cm). The wavenumbers of the (0)
transitions of the =1-0 band are 2612.501350.00033 and
2610.701770.00042 cm () for ArH and
ArH, respectively. The calculated opacity for a gas thermalized at
a temperature of 100 K and a linewidth of 1 km.s of the (0) line is
(ArH). For column densities of
ArH larger than cm, significant absorption
by the (0) line can be expected against bright mid-IR sources
Planetary Nebula Abundances and Morphology: Probing the Chemical Evolution of the Milky Way
This paper presents a homogeneous study of abundances in a sample of 79
northern galactic planetary nebulae whose morphological classes have been
uniformly determined. Ionic abundances and plasma diagnostics were derived from
selected optical line strengths in the literature, and elemental abundances
were estimated with the Ionization Correction Factor developed by Kingsbourgh &
Barlow (1994). We compare the elemental abundances to the final yields obtained
from stellar evolution models of low-and intermediate-mass stars, and we
confirm that most Bipolar planetary nebulae have high nitrogen and helium
abundance, and are the likely progeny of stars with main-sequence mass larger
than 3 solar masses. We derive =0.27, and discuss the implication of such
a high ratio in connection with the solar neon abundance. We determine the
galactic gradients of oxygen and neon, and found Delta log (O/H)/Delta R=-0.01
dex/kpc$ and Delta log (Ne/H)/Delta R=-0.01 dex/kpc. These flat PN gradients do
not reconcile with galactic metallicity gradients flattening with time.Comment: The Astrophysical Journal, in pres
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