1,397 research outputs found
Empirical Tests Of Optimal Cognitive Distance
This article provides empirical tests of the hypothesis of ‘optimal cognitive distance’, proposed by Nooteboom (1999, 2000), in two distinct empirical settings. Variety of cognition, needed for learning, has two dimensions: the number of agents with different cognition, and differences in cognition between them (cognitive distance). The hypothesis is that in interfirm relationships optimal learning entails a trade-off between the advantage of increased cognitive distance for a higher novelty value of a partner’s knowledge, and the disadvantage of less mutual understanding. If the value of learning is the mathematical product of novelty value and understandability, it has an inverse-U shaped relation with cognitive distance, with an optimum level that yields maximal value of learning. With auxiliary hypotheses, the hypothesis is tested on interfirm agreements between pharmaceutical companies and biotech companies, as well as on interfirm agreements in ICT industries.innovation;organizational learning;ICT;biotechnology;alliances
Probing Individual Star Forming Regions Within Strongly Lensed Galaxies at z > 1
Star formation occurs on physical scales corresponding to individual star
forming regions, typically of order ~100 parsecs in size, but current
observational facilities cannot resolve these scales within field galaxies
beyond the local universe. However, the magnification from strong gravitational
lensing allows us to measure the properties of these discrete star forming
regions within galaxies in the distant universe. New results from
multi-wavelength spectroscopic studies of a sample of extremely bright, highly
magnified lensed galaxies are revealing the complexity of star formation on
sub-galaxy scales during the era of peak star formation in the universe. We
find a wide range of properties in the rest-frame UV spectra of individual
galaxies, as well as in spectra that originate from different star forming
regions within the same galaxy. Large variations in the strengths and velocity
structure of Lyman-alpha and strong P Cygni lines such as C IV, and MgII
provide new insights into the astrophysical relationships between extremely
massive stars, the elemental abundances and physical properties of the nebular
gas those stars ionize, and the galactic-scale outflows they power.Comment: 4 pages, 3 figures. To be published in the Proceedings of IAU
Symposium 309. For more details and closely related work see also
arXiv:1310.6695 and arXiv:1406.335
On the lack of correlation between Mg II 2796, 2803 Angstrom and Lyman alpha emission in lensed star-forming galaxies
We examine the Mg II 2796, 2803 Angstrom, Lyman alpha, and nebular line
emission in five bright star-forming galaxies at 1.66<z<1.91 that have been
gravitationally lensed by foreground galaxy clusters. All five galaxies show
prominent Mg II emission and absorption in a P Cygni profile. We find no
correlation between the equivalent widths of Mg II and Lyman alpha emission.
The Mg II emission has a broader range of velocities than do the nebular
emission line profiles; the Mg II emission is redshifted with respect to
systemic by 100 to 200 km/s. When present, Lyman alpha is even more redshifted.
The reddest components of Mg II and Lyman alpha emission have tails to 500-600
km/s, implying a strong outflow. The lack of correlation in the Mg II and Lyman
alpha equivalent widths, the differing velocity profiles, and the high ratios
of Mg II to nebular line fluxes together suggest that the bulk of Mg II
emission does not ultimately arise as nebular line emission, but may instead be
reprocessed stellar continuum emission.Comment: The Astrophysical Journal, in press. 6 pages, 2 figure
Tropical tree cover in a heterogeneous environment: a reaction-diffusion model
This is the final version. Available from Public Library of Science via the DOI in this record.Observed bimodal tree cover distribution sat particular environmental conditions and theoretical models indicate that some areas in the tropics can be in either of the alternative stable vegetation states forest or savanna.However,when including spatial interaction in nonspatial differential equation models of a bistable quantity, only the state with the lowest potential energy remains stable. Our recent reaction-diffusion model of Amazonian tree cover confirmed this and was able to reproduce the observed spatial distribution of forest versus savanna satisfactorily when forced by heterogeneous environmental and anthropogenic variables, even though bistability was underestimated. These conclusions were solely based on simulation results for one set of parameters. Here, we perform ananalytical and numerical analysis of the model. We derive the Maxwell point (MP) of the homogeneous reaction-diffusion equation without savanna trees as a function of rainfall and human impact and show that the front between forest and nonforest settles at this point as long as savanna tree cover near the front remains sufficiently low. For parameters resulting in higher savanna tree cover near the front, we also find irregular forest-savanna cycles and woodland-savanna bistability, which can both explain the remaining observed bimodality.EPSR
Stellar Populations of Highly Magnified Lensed Galaxies: Young Starbursts at z~2
We present a comprehensive analysis of the rest-frame UV to near-IR spectral
energy distributions and rest-frame optical spectra of four of the brightest
gravitationally lensed galaxies in the literature: RCSGA 032727-132609 at
z=1.70, MS1512-cB58 at z=2.73, SGAS J152745.1+065219 at z=2.76 and SGAS
J122651.3+215220 at z=2.92. This includes new Spitzer imaging for RCSGA0327 as
well as new spectra, near-IR imaging and Spitzer imaging for SGAS1527 and
SGAS1226. Lensing magnifications of 3-4 magnitudes allow a detailed study of
the stellar populations and physical conditions. We compare star formation
rates as measured from the SED fit, the H-alpha and [OII] emission lines, and
the UV+IR bolometric luminosity where 24 micron photometry is available. The
SFR estimate from the SED fit is consistently higher than the other indicators,
which suggests that the Calzetti dust extinction law used in the SED fitting is
too flat for young star-forming galaxies at z~2. Our analysis finds similar
stellar population parameters for all four lensed galaxies: stellar masses
3-7*10^9 M_sun, young ages ~ 100 Myr, little dust content E(B-V)=0.10-0.25, and
star formation rates around 20-100 M_sun/yr. Compared to typical values for the
galaxy population at z~2, this suggests we are looking at newly formed,
starbursting systems that have only recently started the build-up of stellar
mass. These results constitute the first detailed, uniform analysis of a sample
of the growing number of strongly lensed galaxies known at z~2.Comment: 13 pages, 8 figures, Accepted to Ap
Spatially Resolved Galactic Wind in Lensed Galaxy RCSGA 032727-132609
We probe the spatial distribution of outflowing gas along four lines of sight
separated by up to 6 kpc in a gravitationally-lensed star-forming galaxy at
z=1.70. Using MgII and FeII emission and absorption as tracers, we find that
the clumps of star formation are driving galactic outflows with velocities of
-170 to -250 km/sec. The velocities of MgII emission are redshifted with
respect to the systemic velocities of the galaxy, consistent with being
back-scattered. By contrast, the FeII fluorescent emission lines are either
slightly blueshifted or at the systemic velocity of the galaxy. Taken together,
the velocity structure of the MgII and FeII emission is consistent with arising
through scattering in galactic winds. Assuming a thin shell geometry for the
out owing gas, the estimated masses carried out by these outfows are large (>
30 - 50 ), with mass loading factors several times the
star-formation rate. Almost 20% to 50% of the blueshifted absorption probably
escapes the gravitational potential of the galaxy. In this galaxy, the outflow
is "locally sourced", that is, the properties of the outflow in each line of
sight are dominated by the properties of the nearest clump of star formation;
the wind is not global to the galaxy. The mass outflow rates and the momentum
flux carried out by outflows in individual star forming knots of this object
are comparable to that of starburst galaxies in the local Universe.Comment: 19 pages, 10 figure, accepted for publication in MNRA
FIREWORKS U38-to-24 micron photometry of the GOODS-CDFS: multi-wavelength catalog and total IR properties of distant Ks-selected galaxies
We present a Ks-selected catalog, dubbed FIREWORKS, for the Chandra Deep
Field South (CDFS) containing photometry in U_38, B_435, B, V, V_606, R, i_775,
I, z_850, J, H, Ks, [3.6 um], [4.5 um], [5.8 um], [8.0 um], and the MIPS [24
um] band. The imaging has a typical Ks limit of 24.3 mag (5 sigma, AB) and
coverage over 113 arcmin^2 in all bands and 138 arcmin^2 in all bands but H. We
cross-correlate our catalog with the 1 Ms X-ray catalog by Giacconi et al.
(2002) and with all available spectroscopic redshifts to date. We find and
explain systematic differences in a comparison with the 'z_850 + Ks'-selected
GOODS-MUSIC catalog that covers ~90% of the field. We exploit the U38-to-24
micron photometry to determine which Ks-selected galaxies at 1.5<z<2.5 have the
brightest total IR luminosities and which galaxies contribute most to the
integrated total IR emission. The answer to both questions is that red galaxies
are dominating in the IR. This is true no matter whether color is defined in
the rest-frame UV, optical, or optical-to-NIR. We do find however that among
the reddest galaxies in the rest-frame optical, there is a population of
sources with only little mid-IR emission, suggesting a quiescent nature.Comment: Accepted for publication in the Astrophysical Journal, 20 pages, 10
figures, reference to website correcte
The Mass Distribution of the Strong Lensing Cluster SDSS J1531+3414
We present the mass distribution at the core of SDSS J1531+3414, a
strong-lensing cluster at z=0.335. We find that the mass distribution is well
described by two cluster-scale halos with a contribution from cluster-member
galaxies. New HST observations of SDSS J1531+3414 reveal a signature of ongoing
star formation associated with the two central galaxies at the core of the
cluster, in the form of a chain of star forming regions at the center of the
cluster. Using the lens model presented here, we place upper limits on the
contribution of a possible lensed image to the flux at the center region, and
rule out that this emission is coming from a background source.Comment: 8 pages, 5 figures; Submitted to Ap
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