416 research outputs found
Strategic Operations Research and the Edelman Prize Finalist Applications 1989-1998
In an earlier study we examined the available evidence on the Edelman Prize finalist applications 1989-1998. This study concluded that 13 of the 42 private sector applications provide examples of strategic operations research (SOR) when SOR is defined as operations research that creates a sustainable competitive advantage. In a follow-up study we tested our classifications, gathering longitudinal information on the continued success of the Edelman applications. We contacted people who were familiar with all the private sector applications that were Edelman finalists 1989-1996 and had at least five years of history since the competition. We describe the post-Edelman history of these applications and use this data to reassess their strategic role. We found that the longitudinal data provides evidence to support our original classification, but also suggests that several additional applications were more strategic than was originally apparent. We conclude that almost 60% (20 of 34) of these applications created a sustainable competitive advantage for their firms and provide examples of SOR
Observations of Rapid Disk-Jet Interaction in the Microquasar GRS 1915+105
We present evidence that ~ 30 minute episodes of jet formation in the
Galactic microquasar GRS 1915+105 may sometimes entirely be a superposition of
smaller, faster phenomena. We base this conclusion on simultaneous X-ray and
infrared observations in July 2002, using the Rossi X-ray Timing Explorer and
the Palomar 5 meter telescope. On two nights, we observed quasi-periodic
infrared flares from GRS 1915+105, each accompanied by a set of fast
oscillations in the X-ray light curve (indicating an interaction between the
jet and accretion disk). In contrast to similar observations in 1997, we find
that the duration of each X-ray cycle matches the duration of its accompanying
infrared flare, and we observed one instance in which an isolated X-ray
oscillation occurred at the same time as a faint infrared "subflare" (of
duration ~ 150 seconds) superimposed on one of the main flares. From these
data, we are able to conclude that each X-ray oscillation had an associated
faint infrared flare and that these flares blend together to form, and entirely
comprise, the ~ 30 minute events we observed. Part of the infrared emission in
1997 also appears to be due to superimposed small flares, but it was
overshadowed by infrared-bright ejections associated with the appearance of a
sharp "trigger" spike in each X-ray cycle that were not present in 2002. We
also study the evolution of the X-ray spectrum and find significant differences
in the high energy power law component, which was strongly variable in 1997 but
not in 2002. Taken together, these observations reveal the diversity of ways in
which the accretion disk and jet in black hole systems are capable of
interacting and solidify the importance of the trigger spike for large
ejections to occur on ~ 30 minute timescales in GRS 1915+105.Comment: 17 pages, 9 figures; accepted for publication in The Astrophysical
Journa
UV Absorption Lines from High-Velocity Gas in the Vela Supernova Remnant: New insights from STIS Echelle Observations of HD72089
The star HD72089 is located behind the Vela supernova remnant and shows a
complex array of high and low velocity interstellar absorption features arising
from shocked clouds. A spectrum of this star was recorded over the wavelength
range 1196.4 to 1397.2 Angstroms at a resolving power lambda/Delta lambda =
110,000 and signal-to-noise ratio of 32 by STIS on the Hubble Space Telescope.
We have identified 7 narrow components of C I and have measured their relative
populations in excited fine-structure levels. Broader features at heliocentric
velocities ranging from -70 to +130 km/s are seen in C II, N I, O I, Si II, S
II and Ni II. In the high-velocity components, the unusually low abundances of
N I and O I, relative to S II and Si II, suggest that these elements may be
preferentially ionized to higher stages by radiation from hot gas immediately
behind the shock fronts.Comment: 11 pages, 2 figures, Latex. Submitted for the special HST ERO issue
of the Astrophysical Journal Letter
23 High Redshift Supernovae from the IfA Deep Survey: Doubling the SN Sample at z>0.7
We present photometric and spectroscopic observations of 23 high redshift
supernovae spanning a range of z=0.34-1.03, 9 of which are unambiguously
classified as Type Ia. These supernovae were discovered during the IfA Deep
Survey, which began in September 2001 and observed a total of 2.5 square
degrees to a depth of approximately m=25-26 in RIZ over 9-17 visits, typically
every 1-3 weeks for nearly 5 months, with additional observations continuing
until April 2002. We give a brief description of the survey motivations,
observational strategy, and reduction process. This sample of 23 high-redshift
supernovae includes 15 at z>0.7, doubling the published number of objects at
these redshifts, and indicates that the evidence for acceleration of the
universe is not due to a systematic effect proportional to redshift. In
combination with the recent compilation of Tonry et al. (2003), we calculate
cosmological parameter density contours which are consistent with the flat
universe indicated by the CMB (Spergel et al. 2003). Adopting the constraint
that Omega_total = 1.0, we obtain best-fit values of (Omega_m,
Omega_Lambda)=(0.33, 0.67) using 22 SNe from this survey augmented by the
literature compilation. We show that using the empty-beam model for
gravitational lensing does not eliminate the need for Omega_Lambda > 0.
Experience from this survey indicates great potential for similar large-scale
surveys while also revealing the limitations of performing surveys for z>1 SNe
from the ground.Comment: 67 pages, 12 figures, 12 tables, accepted for publication in the
Astrophysical Journa
Cytokine responses in birds challenged with the human food-borne pathogen Campylobacter jejuni implies a Th17 response
Development of process orientated understanding of cytokine interactions within the gastrointestinal tract during an immune response to pathogens requires experimentation and statistical modelling. The immune response against pathogen challenge depends on the specific threat to the host. Here, we show that broiler chickens mount a breed-dependent immune response to Campylobacter jejuni infection in the caeca by analysing experimental data using frequentist and Bayesian structural equation models (SEM). SEM provides a framework by which cytokine interdependencies, based on prior knowledge, can be tested. In both breeds important cytokines including pro-inflammatory interleukin (IL)-1β, , IL-4, IL-17A, interferon (IFN)-γ and anti-inflammatory IL-10 and transforming growth factor (TGF)-β4 were expressed post-challenge. The SEM revealed a putative regulatory pathway illustrating a T helper (Th)17 response and regulation of IL-10, which is breed-dependent. The prominence of the Th17 pathway indicates the cytokine response aims to limit the invasion or colonization of an extracellular bacterial pathogen but the time-dependent nature of the response differs between breeds
LoCuSS: A Comparison of Sunyaev-Zel'dovich Effect and Gravitational Lensing Measurements of Galaxy Clusters
We present the first measurement of the relationship between the
Sunyaev-Zel'dovich effect signal and the mass of galaxy clusters that uses
gravitational lensing to measure cluster mass, based on 14 X-ray luminous
clusters at z~0.2 from the Local Cluster Substructure Survey. We measure the
integrated Compton y-parameter, Y, and total projected mass of the clusters
(M_GL) within a projected clustercentric radius of 350 kpc, corresponding to
mean overdensities of 4000-8000 relative to the critical density. We find
self-similar scaling between M_GL and Y, with a scatter in mass at fixed Y of
32%. This scatter exceeds that predicted from numerical cluster simulations,
however, it is smaller than comparable measurements of the scatter in mass at
fixed T_X. We also find no evidence of segregation in Y between disturbed and
undisturbed clusters, as had been seen with T_X on the same physical scales. We
compare our scaling relation to the Bonamente et al. relation based on mass
measurements that assume hydrostatic equilibrium, finding no evidence for a
hydrostatic mass bias in cluster cores (M_GL = 0.98+/-0.13 M_HSE), consistent
with both predictions from numerical simulations and lensing/X-ray-based
measurements of mass-observable scaling relations at larger radii. Overall our
results suggest that the Sunyaev-Zel'dovich effect may be less sensitive than
X-ray observations to the details of cluster physics in cluster cores.Comment: Minor changes to match published version: 2009 ApJL 701:114-11
LoCuSS: The Sunyaev-Zel'dovich Effect and Weak Lensing Mass Scaling Relation
We present the first weak-lensing-based scaling relation between galaxy
cluster mass, M_wl, and integrated Compton parameter Y_sph. Observations of 18
galaxy clusters at z~0.2 were obtained with the Subaru 8.2-m telescope and the
Sunyaev-Zel'dovich Array. The M_wl-Y_sph scaling relations, measured at
Delta=500, 1000, and 2500 rho_c, are consistent in slope and normalization with
previous results derived under the assumption of hydrostatic equilibrium (HSE).
We find an intrinsic scatter in M_wl at fixed Y_sph of 20%, larger than both
previous measurements of M_HSE-Y_sph scatter as well as the scatter in true
mass at fixed Y_sph found in simulations. Moreover, the scatter in our
lensing-based scaling relations is morphology dependent, with 30-40% larger
M_wl for undisturbed compared to disturbed clusters at the same Y_sph at r_500.
Further examination suggests that the segregation may be explained by the
inability of our spherical lens models to faithfully describe the
three-dimensional structure of the clusters, in particular, the structure along
the line-of-sight. We find that the ellipticity of the brightest cluster
galaxy, a proxy for halo orientation, correlates well with the offset in mass
from the mean scaling relation, which supports this picture. This provides
empirical evidence that line-of-sight projection effects are an important
systematic uncertainty in lensing-based scaling relations.Comment: Accepted versio
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