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Historia empresarial e historia del trabajo: del aislamiento a la colaboración
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Search for Possible Variation of the Fine Structure Constant
Determination of the fine structure constant alpha and search for its
possible variation are considered. We focus on a role of the fine structure
constant in modern physics and discuss precision tests of quantum
electrodynamics. Different methods of a search for possible variations of
fundamental constants are compared and those related to optical measurements
are considered in detail.Comment: An invited talk at HYPER symposium (Paris, 2002
A Computational Approach for Designing Tiger Corridors in India
Wildlife corridors are components of landscapes, which facilitate the
movement of organisms and processes between intact habitat areas, and thus
provide connectivity between the habitats within the landscapes. Corridors are
thus regions within a given landscape that connect fragmented habitat patches
within the landscape. The major concern of designing corridors as a
conservation strategy is primarily to counter, and to the extent possible,
mitigate the effects of habitat fragmentation and loss on the biodiversity of
the landscape, as well as support continuance of land use for essential local
and global economic activities in the region of reference. In this paper, we
use game theory, graph theory, membership functions and chain code algorithm to
model and design a set of wildlife corridors with tiger (Panthera tigris
tigris) as the focal species. We identify the parameters which would affect the
tiger population in a landscape complex and using the presence of these
identified parameters construct a graph using the habitat patches supporting
tiger presence in the landscape complex as vertices and the possible paths
between them as edges. The passage of tigers through the possible paths have
been modelled as an Assurance game, with tigers as an individual player. The
game is played recursively as the tiger passes through each grid considered for
the model. The iteration causes the tiger to choose the most suitable path
signifying the emergence of adaptability. As a formal explanation of the game,
we model this interaction of tiger with the parameters as deterministic finite
automata, whose transition function is obtained by the game payoff.Comment: 12 pages, 5 figures, 6 tables, NGCT conference 201
NACO Polarimetric Differential Imaging of TW Hya: A Sharp Look at the Closest T Tauri Disk
We present high-contrast imaging data on the disk of the classical T Tauri
star TW Hya. The images were obtained through the polarimetric differential
imaging technique with the adaptive optics system NACO. Our commissioning data
show the presence of polarized disk emission between 0.1" and 1.4" from the
star. We derive the first Ks-band radial polarized intensity distribution. We
show that the polarized intensity compares well to shorter wavelengths surface
brightness observations and confirm the previously reported gradual slope
change around 0.8". These results show the potential of the new polarimetric
differential imaging technique at 8m-class telescopes to map the inner regions
of protoplanetary disks.Comment: Accepted for publication in Astronomy & Astrophysics; 7 pages, 7
figure
The merger of vertically offset quasi-geostrophic vortices
We examine the critical merging distance between two equal-volume, equal-potential-vorticity quasi-geostrophic vortices. We focus on how this distance depends on the vertical offset between the two vortices, each having a unit mean height-to-width aspect ratio. The vertical direction is special in the quasi-geostrophic model (used to capture the leading-order dynamical features of stably stratified and rapidly rotating geophysical flows) since vertical advection is absent. Nevertheless vortex merger may still occur by horizontal advection. In this paper, we first investigate the equilibrium states for the two vortices as a function of their vertical and horizontal separation. We examine their basic properties together with their linear stability. These findings are next compared to numerical simulations of the nonlinear evolution of two spheres of potential vorticity. Three different regimes of interaction are identified, depending on the vertical offset. For a small offset, the interaction differs little from the case when the two vortices are horizontally aligned. On the other hand, when the vertical offset is comparable to the mean vortex radius, strong interaction occurs for greater horizontal gaps than in the horizontally aligned case, and therefore at significantly greater full separation distances. This perhaps surprising result is consistent with the linear stability analysis and appears to be a consequence of the anisotropy of the quasi-geostrophic equations. Finally, for large vertical offsets, vortex merger results in the formation of a metastable tilted dumbbell vortex.Publisher PDFPeer reviewe
Factor H autoantibody is associated with atypical hemolytic uremic syndrome in children in the United Kingdom and Ireland
Factor H autoantibodies can impair complement
regulation, resulting in atypical hemolytic uremic
syndrome, predominantly in childhood. There are no trials
investigating treatment, and clinical practice is only
informed by retrospective cohort analysis. Here we
examined 175 children presenting with atypical hemolytic
uremic syndrome in the United Kingdom and Ireland for
factor H autoantibodies that included 17 children with
titers above the international standard. Of the 17, seven
had a concomitant rare genetic variant in a gene encoding
a complement pathway component or regulator. Two
children received supportive treatment; both developed
established renal failure. Plasma exchange was associated
with a poor rate of renal recovery in seven of 11 treated. Six
patients treated with eculizumab recovered renal function.
Contrary to global practice, immunosuppressive therapy to
prevent relapse in plasma exchange–treated patients was
not adopted due to concerns over treatment-associated
complications. Without immunosuppression, the relapse
rate was high (five of seven). However, reintroduction of
treatment resulted in recovery of renal function. All
patients treated with eculizumab achieved sustained
remission. Five patients received renal transplants without
specific factor H autoantibody–targeted treatment with
recurrence in one who also had a functionally significant CFI mutation. Thus, our current practice is to initiate
eculizumab therapy for treatment of factor H
autoantibody–mediated atypical hemolytic uremic
syndrome rather than plasma exchange with or without
immunosuppression. Based on this retrospective analysis
we see no suggestion of inferior treatment, albeit the
strength of our conclusions is limited by the small sample siz
Organism-sediment interactions govern post-hypoxia recovery of ecosystem functioning
Hypoxia represents one of the major causes of biodiversity and ecosystem functioning loss for coastal waters. Since eutrophication-induced hypoxic events are becoming increasingly frequent and intense, understanding the response of ecosystems to hypoxia is of primary importance to understand and predict the stability of ecosystem functioning. Such ecological stability may greatly depend on the recovery patterns of communities and the return time of the system properties associated to these patterns. Here, we have examined how the reassembly of a benthic community contributed to the recovery of ecosystem functioning following experimentally-induced hypoxia in a tidal flat. We demonstrate that organism-sediment interactions that depend on organism size and relate to mobility traits and sediment reworking capacities are generally more important than recovering species richness to set the return time of the measured sediment processes and properties. Specifically, increasing macrofauna bioturbation potential during community reassembly significantly contributed to the recovery of sediment processes and properties such as denitrification, bedload sediment transport, primary production and deep pore water ammonium concentration. Such bioturbation potential was due to the replacement of the small-sized organisms that recolonised at early stages by large-sized bioturbating organisms, which had a disproportionately stronger influence on sediment. This study suggests that the complete recovery of organism-sediment interactions is a necessary condition for ecosystem functioning recovery, and that such process requires long periods after disturbance due to the slow growth of juveniles into adult stages involved in these interactions. Consequently, repeated episodes of disturbance at intervals smaller than the time needed for the system to fully recover organism-sediment interactions may greatly impair the resilience of ecosystem functioning.
A DNA Barcode Library for North American Ephemeroptera: Progress and Prospects
DNA barcoding of aquatic macroinvertebrates holds much promise as a tool for taxonomic research and for providing the reliable identifications needed for water quality assessment programs. A prerequisite for identification using barcodes is a reliable reference library. We gathered 4165 sequences from the barcode region of the mitochondrial cytochrome c oxidase subunit I gene representing 264 nominal and 90 provisional species of mayflies (Insecta: Ephemeroptera) from Canada, Mexico, and the United States. No species shared barcode sequences and all can be identified with barcodes with the possible exception of some Caenis. Minimum interspecific distances ranged from 0.3–24.7% (mean: 12.5%), while the average intraspecific divergence was 1.97%. The latter value was inflated by the presence of very high divergences in some taxa. In fact, nearly 20% of the species included two or three haplotype clusters showing greater than 5.0% sequence divergence and some values are as high as 26.7%. Many of the species with high divergences are polyphyletic and likely represent species complexes. Indeed, many of these polyphyletic species have numerous synonyms and individuals in some barcode clusters show morphological attributes characteristic of the synonymized species. In light of our findings, it is imperative that type or topotype specimens be sequenced to correctly associate barcode clusters with morphological species concepts and to determine the status of currently synonymized species
The XMM-Newton Serendipitous Source Catalogue
We describe the production, properties and scientific potential of the
XMM-Newton catalogue of serendipitous X-ray sources. The first version of this
catalogue is nearing completion and is planned to be released before the end of
2002.Comment: Proceedings of the "X-ray surveys, in the light of the new
observatories" workshop, Astronomische Nachrichten, in the press (4 pages, 3
eps figures, uses an.cls
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