652 research outputs found
Amalgamated products and properly 3-realizable groups
In this paper, we show that the class of all properly 3-realizable groups is
closed under amalgamated free products (and HNN-extensions) over finite groups.
We recall that is said to be properly 3-realizable if there exists a
compact 2-polyhedron with and whose universal cover
has the proper homotopy type of a 3-manifold (with boundary).Comment: J. Pure Appl. Alg., to appea
Elevated immune gene expression is associated with poor reproductive success of urban blue tits
Urban and forest habitats differ in many aspects that can lead to modifications of the immune system of wild animals. Altered parasite communities, pollution, and artificial light at night in cities have been associated with exacerbated inflammatory responses, with possibly negative fitness consequences, but few data are available from free-living animals. Here, we investigate how urbanization affects major immune pathways and experimentally test potentially contributing factors in blue tits (Cyanistes caeruleus) from an urban and forest site. We first compared breeding adults by quantifying the mRNA transcript levels of proteins associated with anti-bacterial, anti-malarial (TLR4, LY86) and anti-helminthic (Type 2 transcription factor GATA3) immune responses. Adult urban and forest blue tits differed in gene expression, with significantly increased TLR4 and GATA3, but not LY86, in the city. We then experimentally tested whether these differences were environmentally induced by cross-fostering eggs between the sites and measuring mRNA transcripts in nestlings. The populations differed in reduced reproductive success, with a lower fledging success and lower fledgling weight recorded at the urban site. This mirrors the findings of our twin study reporting that the urban site was severely resource limited when compared to the forest. Because of low urban survival, robust gene expression data were only obtained from nestlings reared in the forest. Transcript levels in these nestlings showed no (TLR4, LY86), or weak (GATA3), differences according to their origin from forest or city nests, suggesting little genetic or maternal contribution to nestling immune transcript levels. Lastly, to investigate differences in parasite pressure between urban and forest sites, we measured the prevalence of malaria in adult and nestling blood. Prevalence was invariably high across environments and not associated with the transcript levels of the studied immune genes. Our results support the hypothesis that inflammatory pathways are activated in an urban environment and suggest that these differences are most likely induced by environmental factors
Integrated behavioural and stable isotope data reveal altered diet linked to low breeding success in urban-dwelling blue tits (Cyanistes caeruleus)
Animals often show reduced reproductive success in urban compared to adjacent natural areas. The lower availability and quality of natural food in cities is suggested as one key limiting factor. However, only few studies have provided conclusive support by simultaneously assessing food availability, diet and fitness. We consolidate this evidence by taking a holistic approach, comparing blue tits breeding in forest, suburban and urban areas. We (a) assessed arthropod availability, (b) investigated parental provisioning behaviour, (c) inferred diet through stable isotope analysis, and (d) measured reproductive success. At the urban site, we found a significant reduction in caterpillar availability, the main food source of blue tits, and consequently urban tits fed their offspring with fewer caterpillars than forest and suburban birds. Stable isotope analysis confirmed that diet in the urban area was fundamentally different than in the other sites. Reproductive success was lower in both urban and suburban sites compared to the forest site, and was positively associated with volume of provisioned caterpillars. Our findings provide strong integrative evidence that urban blue tit nestlings are not receiving a suitable diet, and this may be an important limiting factor for urban populations of this and potentially many other species
Commissioning and experience in stripping, filtering and measuring the 4.2 MeV/u lead ion beam at CERN Linac 3
The new CERN Heavy Ion Linac (Linac3) accelerates a Pb27+ beam to 4.2 MeV/u. The beam is then stripped to Pb53+ by a carbon foil, and, after stripping, a 12 m filter line prepares the beam for the injection into the Proton Synchrotron Booster (PSB). The filter line eliminates the unwanted charge states, checks the beam quality (energy, energy spread, transverse emittance and intensity), and finally transports the beam in the lines leading to the PSB. The paper summarises the transverse beam dynamics of the line, and reports on its commissioning, especially focusing on the experiments that led to the stripper choice, and on the measurements performed with a specially developed single pulse moperational experience is also reported
Weak -structures and one-relator groups
Motivated by the notion of boundary for hyperbolic and groups, M.
Bestvina in "Local Homology Properties of Boundaries of Groups" introduced the
notion of a (weak) -structure and (weak) -boundary for
a group of type (i.e., having a finite complex), with
implications concerning the Novikov conjecture for . Since then, some
classes of groups have been shown to admit a weak -structure (see
"Weak -structures for some classes of groups" by C.R. Guilbault for
example), but the question whether or not every group of type
admits such a structure remains open. In this paper, we show that every torsion
free one-relator group admits a weak -structure, by showing that
they are all properly aspherical at infinity; moreover, in the -ended case
the corresponding weak -boundary has the shape of either a circle
or a Hawaiian earring depending on whether the group is a virtually surface
group or not. Finally, we extend this result to a wider class of groups still
satisfying a Freiheitssatz property
The dynamics and mixing of small spherical particles in a plane, free shear layer
The equation of motion of small rigid spheres settling under gravity in a two-dimensional
inviscid flow given by the Stuart solution of the Euler equations is analyzed as a fourdimensional dynamical system. It is shown that depending on the values of the Stokes,
Grashof, and a scaled Reynolds number, particles may either sediment or remain permanently
suspended in the flow. When suspension occurs, the particle trajectories are shown to be
attracted by a single period, quasiperiodic, or chaotic orbits. A consequence of the existence of
a strange attractor (chaotic orbit) is that heavy particles can reach a stage ofjhdization by
which they remain indefinitely suspended in a layer of finite height located above the center of
the Stuart vortices.Secretaria de Estado de Universidades e Investigación de España FPU-2868794
Rauch-Tung-Striebel Smoother for Position Estimation of Short-Stroke Reluctance Actuators
This article presents a novel state estimator for short-stroke reluctance actuators, intended for soft-landing control applications in which the position cannot be measured in real time. One of the most important contributions regards the system modeling for the estimator. The discrete state of the hybrid system is treated as an input. Moreover, the model is simplified to facilitate the identification of parameters and the implementation of the estimator. Thus, auxiliary variables are added to the state vector in order to indirectly account for modeling errors. Another important contribution is the state estimation approach. It is based on the Rauch–Tung–Striebel fixed-interval smoother, which allows refining past data from later observations. Numerous simulations are performed to analyze and compare the proposal and several alternatives. In addition, experimental testing is presented to evaluate and validate the estimator. As the simulated and experimental analyses demonstrate, the combined effect of the novel additions results in significantly smaller estimation errors of position and velocity
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