77 research outputs found
Juvenile morphology of the large Antarctic canopy-forming brown alga, Desmarestia menziesii J. Agardh
Open Access via Springer Compact Agreement. We are grateful to the UK Natural Environment Research Council for funding to FCK (grants NE/D521522/1 and NE/J023094/1), in particular through the Collaborative Antarctic Science Scheme (Grant CASS-134, 2017) to FCK and LSP. Funding for cruise-based observations in 2019 was from US National Science Foundation award OPP-1744550 to CDA. We thank Kate Stanton, Teresa Murphy and Ben Robinson (British Antarctic Survey) for support with diving operations around Rothera in January–February 2018, and also Richard L. Moe (UC Berkeley) for locating specimens corresponding to the morphology described here in the UC collection. Special thanks are due to Charlie Bibby (Financial Times) for taking professional photographs of the unknown Desmarestia sp. in the aquarium of the Bonner Lab at Rothera (Fig. 2a). We would also like to thank Richard L. Moe (UC Berkeley) and Christian Wiencke (AWI Bremerhaven) for their very helpful reviews of this paper. Also, the MASTS pooling initiative (Marine Alliance for Science and Technology for Scotland, funded by the Scottish Funding Council and contributing institutions; grant reference HR09011) is gratefully acknowledged for supporting FCK. This research contributes to the SCAR Ant-ERA research programme.Peer reviewedPublisher PD
Markov dynamics as a zooming lens for multiscale community detection: non clique-like communities and the field-of-view limit
In recent years, there has been a surge of interest in community detection
algorithms for complex networks. A variety of computational heuristics, some
with a long history, have been proposed for the identification of communities
or, alternatively, of good graph partitions. In most cases, the algorithms
maximize a particular objective function, thereby finding the `right' split
into communities. Although a thorough comparison of algorithms is still
lacking, there has been an effort to design benchmarks, i.e., random graph
models with known community structure against which algorithms can be
evaluated. However, popular community detection methods and benchmarks normally
assume an implicit notion of community based on clique-like subgraphs, a form
of community structure that is not always characteristic of real networks.
Specifically, networks that emerge from geometric constraints can have natural
non clique-like substructures with large effective diameters, which can be
interpreted as long-range communities. In this work, we show that long-range
communities escape detection by popular methods, which are blinded by a
restricted `field-of-view' limit, an intrinsic upper scale on the communities
they can detect. The field-of-view limit means that long-range communities tend
to be overpartitioned. We show how by adopting a dynamical perspective towards
community detection (Delvenne et al. (2010) PNAS:107: 12755-12760; Lambiotte et
al. (2008) arXiv:0812.1770), in which the evolution of a Markov process on the
graph is used as a zooming lens over the structure of the network at all
scales, one can detect both clique- or non clique-like communities without
imposing an upper scale to the detection. Consequently, the performance of
algorithms on inherently low-diameter, clique-like benchmarks may not always be
indicative of equally good results in real networks with local, sparser
connectivity.Comment: 20 pages, 6 figure
CMB-S4: Forecasting Constraints on Primordial Gravitational Waves
CMB-S4---the next-generation ground-based cosmic microwave background (CMB)
experiment---is set to significantly advance the sensitivity of CMB
measurements and enhance our understanding of the origin and evolution of the
Universe, from the highest energies at the dawn of time through the growth of
structure to the present day. Among the science cases pursued with CMB-S4, the
quest for detecting primordial gravitational waves is a central driver of the
experimental design. This work details the development of a forecasting
framework that includes a power-spectrum-based semi-analytic projection tool,
targeted explicitly towards optimizing constraints on the tensor-to-scalar
ratio, , in the presence of Galactic foregrounds and gravitational lensing
of the CMB. This framework is unique in its direct use of information from the
achieved performance of current Stage 2--3 CMB experiments to robustly forecast
the science reach of upcoming CMB-polarization endeavors. The methodology
allows for rapid iteration over experimental configurations and offers a
flexible way to optimize the design of future experiments given a desired
scientific goal. To form a closed-loop process, we couple this semi-analytic
tool with map-based validation studies, which allow for the injection of
additional complexity and verification of our forecasts with several
independent analysis methods. We document multiple rounds of forecasts for
CMB-S4 using this process and the resulting establishment of the current
reference design of the primordial gravitational-wave component of the Stage-4
experiment, optimized to achieve our science goals of detecting primordial
gravitational waves for at greater than , or, in the
absence of a detection, of reaching an upper limit of at CL.Comment: 24 pages, 8 figures, 9 tables, submitted to ApJ. arXiv admin note:
text overlap with arXiv:1907.0447
Insights into the high-energy γ-ray emission of Markarian 501 from extensive multifrequency observations in the Fermi era
We report on the γ-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) γ-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 ± 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 ± 0.14, and the softest one is 2.51 ± 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15-August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size ≲0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (≃1044 erg s-1) constitutes only a small fraction (∼10-3) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude. © 2011. The American Astronomical Society
CMB-S4: Forecasting Constraints on Primordial Gravitational Waves
Abstract: CMB-S4—the next-generation ground-based cosmic microwave background (CMB) experiment—is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the universe. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semianalytic projection tool, targeted explicitly toward optimizing constraints on the tensor-to-scalar ratio, r, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2–3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments, given a desired scientific goal. To form a closed-loop process, we couple this semianalytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for r > 0.003 at greater than 5σ, or in the absence of a detection, of reaching an upper limit of r < 0.001 at 95% CL
CMB-S4
We describe the stage 4 cosmic microwave background ground-based experiment CMB-S4
New directions for program evaluation
Publ. comme no 61, spring 1994 de la revue New directions for program evaluationBibliogr. à la fin des textesIndex: p. 93-9
Más allá de los métodos cualitativos versus los cuantitativos
The present article�s goal is to suggest that, partly, the present discussion about qualitative and
quantitative methods does not focus on productive questions and therefore it is not discussed as
logically as it could be. This article does not suggest that a full resolution of the methodological
argument is possible. This debate, as it is approached, darkens issues and creates discord between both
methods, instead of building bridges that allow a clarification of the original disagreements. The
offered solution implies a recognition of the debate as wrongly conducted. It is not necessary to
choose between two methods or paradigms. This work offers some of the reasons that justify a joint
use in order to satisfy the evaluative investigation demands.El objetivo del presente artículo es sugerir que, en parte, el debate actual sobre métodos
cualitativos y cuantitativos no se centra en cuestiones fructíferas y, por tanto, no se discute tan
lógicamente como se debería. Con este artículo no se intenta sugerir que sea posible una resolución
completa de esta disputa metodológica. El debate, tal como está siendo planteado, esta oscureciendo
las cuestiones y creando cismas entre los dos métodos, cuando deberían construirse puentes que
permitan clarificar los desacuerdos originarios. La solución planteada estaría en darse cuenta que el
debate está incorrectamente planteado. No es necesario elegir entre los dos métodos o entre los dos
paradigmas. En este trabajo se plantean algunas de las razones que llevan a pensar que lo lógico sería
ultilizarlos conjuntamente para satisfacer las exigencias que se presenten en la investigación
evaluativa
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