862 research outputs found
Conditions for the equivalence between IQC and graph separation stability results
This paper provides a link between time-domain and frequency-domain stability
results in the literature. Specifically, we focus on the comparison between
stability results for a feedback interconnection of two nonlinear systems
stated in terms of frequency-domain conditions. While the Integral Quadratic
Constrain (IQC) theorem can cope with them via a homotopy argument for the
Lurye problem, graph separation results require the transformation of the
frequency-domain conditions into truncated time-domain conditions. To date,
much of the literature focuses on "hard" factorizations of the multiplier,
considering only one of the two frequency-domain conditions. Here it is shown
that a symmetric, "doubly-hard" factorization is required to convert both
frequency-domain conditions into truncated time-domain conditions. By using the
appropriate factorization, a novel comparison between the results obtained by
IQC and separation theories is then provided. As a result, we identify under
what conditions the IQC theorem may provide some advantage
Gemini Frontier Fields: Wide-field Adaptive Optics -band Imaging of the Galaxy Clusters MACS J0416.1-2403 and Abell 2744
We have observed two of the six Frontier Fields galaxy clusters, MACS
J0416.1-2403 and Abell 2744, using the Gemini Multi-Conjugate Adaptive Optics
System (GeMS) and the Gemini South Adaptive Optics Imager (GSAOI). With
0.08"-0.10" FWHM our data are nearly diffraction-limited over a 100"x100" wide
area. GeMS/GSAOI complements the Hubble Space Telescope (HST) redwards of
1.6microns with twice the angular resolution. We reach a 5 sigma depth of Ks =
25.6 mag (AB) for compact sources. In this paper we describe the observations,
the data processing and the initial public data release. We provide fully
calibrated, co-added images matching the native GSAOI pixel scale as well as
the larger plate scales of the HST release, adding to the legacy value of the
Frontier Fields. Our work demonstrates that even for fields at high galactic
latitude, where natural guide stars are rare, current multi-conjugated adaptive
optics technology at 8m-telescopes has opened a new window on the distant
Universe. Observations of a third Frontier Field, Abell 370, are planned.Comment: Accepted for publication in ApJS; significantly revised compared to
the first submissio
First performance of the gems + gmos system. Part1. Imaging
During the commissioning of the Gemini MCAO System (GeMS), we had the
opportunity to obtain data with the Gemini Multi-Object Spectrograph (GMOS),
the most utilised instrument at Gemini South Observatory, in March and May
2012. Several globular clusters were observed in imaging mode that allowed us
to study the performance of this new and untested combination. GMOS is a
visible instrument, hence pushing MCAO toward the visible.We report here on the
results with the GMOS instruments, derive photometric performance in term of
Full Width Half Maximum (FWHM) and throughput. In most of the cases, we
obtained an improvement factor of at least 2 against the natural seeing. This
result also depends on the Natural Guide Star constellation selected for the
observations and we then study the impact of the guide star selection on the
FWHM performance.We also derive a first astrometric analysis showing that the
GeMS+GMOS system provide an absolute astrometric precision better than 8mas and
a relative astrometric precision lower than 50 mas.Comment: 13 pages, 11 figures, accepted for publication in MNRAS on March 23rd
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The first influenza pandemic in the new millennium: lessons learned hitherto for current control efforts and overall pandemic preparedness
Influenza viruses pose a permanent threat to human populations due to their ability to constantly adapt to impact immunologically susceptible individuals in the forms of epidemic and pandemics through antigenic drifts and antigenic shifts, respectively. Pandemic influenza preparedness is a critical step in responding to future influenza outbreaks. In this regard, responding to the current pandemic and preparing for future ones requires critical planning for the early phases where there is no availability of pandemic vaccine with rapid deployment of medical supplies for personal protection, antivirals, antibiotics and social distancing measures. In addition, it has become clear that responding to the current pandemic or preparing for future ones, nation states need to develop or strengthen their laboratory capability for influenza diagnosis as well as begin preparing their vaccine/antiviral deployment plans. Vaccine deployment plans are the critical missing link in pandemic preparedness and response. Rapid containment efforts are not effective and instead mitigation efforts should lead pandemic control efforts. We suggest that development of vaccine/antiviral deployment plans is a key preparedness step that allows nations identify logistic gaps in their response capacity
The stellar mass - size relation for cluster galaxies at z=1 with high angular resolution from the Gemini/GeMS multi-conjugate adaptive optics system
We present the stellar mass - size relation for 49 galaxies within the =
1.067 cluster SPT-CL J05465345, with FWHM 80-120 mas -band data from the Gemini multi-conjugate adaptive optics system
(GeMS/GSAOI). This is the first such measurement in a cluster environment,
performed at sub-kpc resolution at rest-frame wavelengths dominated by the
light of the underlying old stellar populations. The observed stellar mass -
size relation is offset from the local relation by 0.21 dex, corresponding to a
size evolution proportional to , consistent with the literature.
The slope of the stellar mass - size relation = 0.74 0.06,
consistent with the local relation. The absence of slope evolution indicates
that the amount of size growth is constant with stellar mass. This suggests
that galaxies in massive clusters such as SPT-CL J05465345 grow via
processes that increase the size without significant morphological
interference, such as minor mergers and/or adiabatic expansion. The slope of
the cluster stellar mass - size relation is significantly shallower if measured
in /ACS imaging at wavelengths blueward of the Balmer break, similar to
rest-frame UV relations at = 1 in the literature. The stellar mass - size
relation must be measured at redder wavelengths, which are more sensitive to
the old stellar population that dominates the stellar mass of the galaxies. The
slope is unchanged when GeMS -band imaging is degraded to the resolution
of -band HST/NICMOS resolution but dramatically affected when degraded to
-band Magellan/FourStar resolution. Such measurements must be made with AO
in order to accurately characterise the sizes of compact, = 1 galaxies.Comment: 24 pages, 13 figures, 3 tables. Accepted for publication in MNRAS.
Typos corrected, DOI adde
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