5,334 research outputs found
Requisite variety and intercultural teams: to what extent is Ashby's law useful ?
Requisite variety and intercultural teams: To what extent is Ashby's law useful? The “Law of Requisite Variety” (LRV) is frequently evoked to explain the design, functioning and performance of intercultural teams. But to what extent does the law really enhance understanding in this particular field? The authors consider that LRV has rarely been questioned in-depth in management studies. The paper briefly details LRV in the cybernetics context before “translating” it to social systems, organizations and intercultural teams. Using a qualitative case-study method, the case of an intercultural team is analysed and questioned from the perspective of LRV. The results show that LRV superficially fits the composition of this team, but is unable to explain the human and social dynamics that evolve during the work process.law of requisite variety; requisite variety; intercultural teams ; complexity ; diversity; systems; case study
SN 2001em: No Jet-Driven Gamma Ray Burst Event
We report on our second-epoch VLBI and VLA observations of the Type Ib/c
supernova 2001em, five years after the explosion. It was suggested that SN
2001em might be a jet-driven gamma ray burst (GRB), with the jet oriented near
the plane of the sky, which would entail relativistic expansion or motion. Our
VLBI image shows that SN 2001em is still unresolved five years after the
explosion. For a distance of 83 Mpc (H_0 = 70 km/s/Mpc), the nominal expansion
velocity is 5800 +/- 10,000 km/s, and the proper motion is 33,000 +/- 34,000
km/s. Our values are inconsistent with either relativistic expansion or motion,
but are consistent with the non-relativistic expansion speeds and small proper
motions seen in other supernovae. In particular these values are consistent
with radio emission from SN 2001em being due to normal, non-relativistic
supernova ejecta interacting with the circumstellar medium. Our VLA
observations show a power-law decay in flux density since the time of the peak
in the 8.4 GHz radio lightcurve in ~2003.Comment: 5 pages, 2 figs, accepted for publication in ApJ Letters; added
reference
The Proper Motion of PSR J0205+6449 in 3C 58
We report on sensitive phase-referenced and gated 1.4-GHz VLBI radio
observations of the pulsar PSR J0205+6449 in the young pulsar-wind nebula 3C
58, made in 2007 and 2010. We employed a novel technique where the ~105-m Green
Bank telescope is used simultaneously to obtain single-dish data used to
determine the pulsar's period as well as to obtain the VLBI data, allowing the
VLBI correlation to be gated synchronously with the pulse to increase the
signal-to-noise. The high timing noise of this young pulsar precludes the
determination of the proper motion from the pulsar timing. We derive the
position of the pulsar accurate at the milliarcsecond level, which is
consistent with a re-determined position from the Chandra X-ray observations.
We reject the original tentative optical identification of the pulsar by
Shearer and Neustroev (2008), but rather identify a different optical
counterpart on their images, with R-band magnitude ~24. We also determine an
accurate proper motion for PSR J0205+6449 of (2.3 +- 0.3) mas/yr, corresponding
to a projected velocity of only (35 +- 6) km/s for a distance of 3.2 kpc, at
p.a. -38 deg. This projected velocity is quite low compared to the velocity
dispersion of known pulsars of ~200 km/s. Our measured proper motion does not
suggest any particular kinematic age for the pulsar.Comment: 10 pages, 7 figures; accepted for publication in MNRA
The First VLBI Image of the Young, Oxygen-Rich Supernova Remnant in NGC 4449
We report on sensitive 1.4-GHz VLBI radio observations of the unusually
luminous supernova remnant SNR 4449-1 in the galaxy NGC 4449, which gave us the
first well-resolved image of this object. The remnant's radio morphology
consists of two approximately parallel bright ridges, suggesting similarities
to the barrel shape seen for many older Galactic supernova remnants or possibly
to SN 1987A. The angular extent of the remnant is 65 x 40 mas, corresponding to
(3.7 x 2.3) x 10^{18} (D/3.8 Mpc) cm. We also present a new, high
signal-to-noise optical spectrum. By comparing the remnant's linear size to the
maximum velocities measured from optical lines, as well as using constraints
from historical images, we conclude that the supernova explosion occurred
between ~1905 and 1961, likely around 1940. The age of the remnant is therefore
likely ~70 yr. We find that SNR 4449-1's shock wave is likely still interacting
with the circumstellar rather than interstellar medium.Comment: 7 pages, Accepted for publication in MNRA
Requisite variety and intercultural teams: to what extent is Ashby's law useful ?
Cahiers de recherche n° 2009 04 E5Requisite variety and intercultural teams: To what extent is Ashby's law useful? The “Law of Requisite Variety” (LRV) is frequently evoked to explain the design, functioning and performance of intercultural teams. But to what extent does the law really enhance understanding in this particular field? The authors consider that LRV has rarely been questioned in-depth in management studies. The paper briefly details LRV in the cybernetics context before “translating” it to social systems, organizations and intercultural teams. Using a qualitative case-study method, the case of an intercultural team is analysed and questioned from the perspective of LRV. The results show that LRV superficially fits the composition of this team, but is unable to explain the human and social dynamics that evolve during the work process
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