688 research outputs found
Findings of the International Subarachnoid Aneurysm Trial and the National Study of Subarachnoid Haemorrhage in context.
Concern has been expressed about the applicability of the findings of the International Subarachnoid Aneurysm Trial (ISAT) with respect to the relative effects on outcome of coiling and clipping. It has been suggested that the findings of the National Study of Subarachnoid Haemorrhage may have greater relevance for neurosurgical practice. The objective of this paper was to interpret the findings of these two studies in the context of differences in their study populations, design, execution and analysis. Because of differences in design and analysis, the findings of the two studies are not directly comparable. The ISAT analysed all randomized patients by intention-to-treat, including some who did not undergo a repair, and obtained the primary outcome for 99% of participants. The National Study only analysed participants who underwent clipping or coiling, according to the method of repair, and obtained the primary outcome for 91% of participants. Time to repair was also considered differently in the two studies. The comparison between coiling and clipping was susceptible to confounding in the National Study, but not in the ISAT. The two study populations differed to some extent, but inspection of these differences does not support the view that coiling was applied inappropriately in the National Study. Therefore, there are many reasons why the two studies estimated different sizes of effect. The possibility that there were real, systematic differences in practice between the ISAT and the National Study cannot be ruled out, but such explanations must be seen in the context of other explanations relating to chance, differences in design or analysis, or confounding
The Shapes of Cooperatively Rearranging Regions in Glass Forming Liquids
The shapes of cooperatively rearranging regions in glassy liquids change from
being compact at low temperatures to fractal or ``stringy'' as the dynamical
crossover temperature from activated to collisional transport is approached
from below. We present a quantitative microscopic treatment of this change of
morphology within the framework of the random first order transition theory of
glasses. We predict a correlation of the ratio of the dynamical crossover
temperature to the laboratory glass transition temperature, and the heat
capacity discontinuity at the glass transition, Delta C_p. The predicted
correlation agrees with experimental results for the 21 materials compiled by
Novikov and Sokolov.Comment: 9 pages, 6 figure
The influence of fine-scale topography on the impacts of Holocene fire in a Tasmanian montane landscape
Copyright © 2019 John Wiley & Sons, Ltd. Tasmania's montane temperate rainforests contain some of Australia's most ancient and endemic flora. Recent landscape-scale fires have impacted a significant portion of these rainforest ecosystems. The complex and rugged topography of Tasmania results in a highly variable influence of fire across the landscape, rendering predictions of ecosystem response to fire difficult. We assess the role of topographic variation in buffering the influence of fire in these endemic rainforest communities. We developed a new 14000-year (14-ka) palaeoecological dataset from Lake Perry, southern Tasmania, and compared it to neighbouring Lake Osborne
Consensus clustering in complex networks
The community structure of complex networks reveals both their organization
and hidden relationships among their constituents. Most community detection
methods currently available are not deterministic, and their results typically
depend on the specific random seeds, initial conditions and tie-break rules
adopted for their execution. Consensus clustering is used in data analysis to
generate stable results out of a set of partitions delivered by stochastic
methods. Here we show that consensus clustering can be combined with any
existing method in a self-consistent way, enhancing considerably both the
stability and the accuracy of the resulting partitions. This framework is also
particularly suitable to monitor the evolution of community structure in
temporal networks. An application of consensus clustering to a large citation
network of physics papers demonstrates its capability to keep track of the
birth, death and diversification of topics.Comment: 11 pages, 12 figures. Published in Scientific Report
Multiplicity of young brown dwarfs in Cha I
How frequent are brown dwarf binaries? Do brown dwarfs have planets? Are
current theoretical pre-main-sequence evolutionary tracks valid down to the
substellar regime? - Any detection of a companion to a brown dwarf takes us one
step forward towards answering these basic questions of star formation.
We report here on a search for spectroscopic and visual companions to young
brown dwarfs in the Cha I star forming cloud.
Based on spectra taken with UVES at the VLT, we found significant radial
velocity (RV) variations for five bona-fide and candidate brown dwarfs in Cha
I. They can be caused by either a (substellar or planetary) companion or
stellar activity. A companion causing the detected RV variations would have
about a few Jupiter masses. We are planning further UVES observations in order
to explore the nature of the detected RV variations. We also found that the RV
dispersion is only ~ 2km/s indicating that there is probably no run-away brown
dwarf among them.
Additionally a search for companions by direct imaging with the HST and SOFI
(NTT) has yielded to the detection of a few companion candidates in larger
orbits.Comment: Conference proceeding "Origins of stars and planets: The VLT view",
ESO, Garching, April 24-27 200
Quantitation of Cellular Dynamics in Growing Arabidopsis Roots with Light Sheet Microscopy
To understand dynamic developmental processes, living tissues must be imaged
frequently and for extended periods of time. Root development is extensively
studied at cellular resolution to understand basic mechanisms underlying
pattern formation and maintenance in plants. Unfortunately, ensuring continuous
specimen access, while preserving physiological conditions and preventing
photo-damage, poses major barriers to measurements of cellular dynamics in
indeterminately growing organs such as plant roots. We present a system that
integrates optical sectioning through light sheet fluorescence microscopy with
hydroponic culture that enables us to image at cellular resolution a vertically
growing Arabidopsis root every few minutes and for several consecutive days. We
describe novel automated routines to track the root tip as it grows, track
cellular nuclei and identify cell divisions. We demonstrate the system's
capabilities by collecting data on divisions and nuclear dynamics.Comment: * The first two authors contributed equally to this wor
Inference of hidden structures in complex physical systems by multi-scale clustering
We survey the application of a relatively new branch of statistical
physics--"community detection"-- to data mining. In particular, we focus on the
diagnosis of materials and automated image segmentation. Community detection
describes the quest of partitioning a complex system involving many elements
into optimally decoupled subsets or communities of such elements. We review a
multiresolution variant which is used to ascertain structures at different
spatial and temporal scales. Significant patterns are obtained by examining the
correlations between different independent solvers. Similar to other
combinatorial optimization problems in the NP complexity class, community
detection exhibits several phases. Typically, illuminating orders are revealed
by choosing parameters that lead to extremal information theory correlations.Comment: 25 pages, 16 Figures; a review of earlier work
SPECULOOS exoplanet search and its prototype on TRAPPIST
One of the most significant goals of modern science is establishing whether
life exists around other suns. The most direct path towards its achievement is
the detection and atmospheric characterization of terrestrial exoplanets with
potentially habitable surface conditions. The nearest ultracool dwarfs (UCDs),
i.e. very-low-mass stars and brown dwarfs with effective temperatures lower
than 2700 K, represent a unique opportunity to reach this goal within the next
decade. The potential of the transit method for detecting potentially habitable
Earth-sized planets around these objects is drastically increased compared to
Earth-Sun analogs. Furthermore, only a terrestrial planet transiting a nearby
UCD would be amenable for a thorough atmospheric characterization, including
the search for possible biosignatures, with near-future facilities such as the
James Webb Space Telescope. In this chapter, we first describe the physical
properties of UCDs as well as the unique potential they offer for the detection
of potentially habitable Earth-sized planets suitable for atmospheric
characterization. Then, we present the SPECULOOS ground-based transit survey,
that will search for Earth-sized planets transiting the nearest UCDs, as well
as its prototype survey on the TRAPPIST telescopes. We conclude by discussing
the prospects offered by the recent detection by this prototype survey of a
system of seven temperate Earth-sized planets transiting a nearby UCD,
TRAPPIST-1.Comment: Submitted as a chapter in the "Handbook of Exoplanets" (editors: H.
Deeg & J.A. Belmonte; Section Editor: N. Narita). 16 pages, 4 figure
The 2020 Covid-19 pandemic and global value chains
This paper considers the impact of the Covid-19 pandemic on firm strategies and, in particular, the configuration of firms’ global value chains (GVCs) once the pandemic has been brought under control. The merits of alternative location strategies (international diversification vs reshoring) are compared, as are the merits of different governance arrangements (internalization vs externalization) for GVC activities. The possibility of fire-sale foreign direct investment is raised, and the wider geopolitical context is emphasized. The widespread human tragedy is noted, as is the dilemma facing national governments around the world in balancing lives and livelihoods
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