8,007 research outputs found
Dynamics towards the Feigenbaum attractor
We expose at a previously unknown level of detail the features of the
dynamics of trajectories that either evolve towards the Feigenbaum attractor or
are captured by its matching repellor. Amongst these features are the
following: i) The set of preimages of the attractor and of the repellor are
embedded (dense) into each other. ii) The preimage layout is obtained as the
limiting form of the rank structure of the fractal boundaries between attractor
and repellor positions for the family of supercycle attractors. iii) The joint
set of preimages for each case form an infinite number of families of
well-defined phase-space gaps in the attractor or in the repellor. iv) The gaps
in each of these families can be ordered with decreasing width in accord to
power laws and are seen to appear sequentially in the dynamics generated by
uniform distributions of initial conditions. v) The power law with log-periodic
modulation associated to the rate of approach of trajectories towards the
attractor (and to the repellor) is explained in terms of the progression of gap
formation. vi) The relationship between the law of rate of convergence to the
attractor and the inexhaustible hierarchy feature of the preimage structure is
elucidated.Comment: 8 pages, 12 figure
Do columnar defects produce bulk pinning?
From magneto-optical imaging performed on heavy-ion irradiated YBaCuO single
crystals, it is found that at fields and temperatures where strong single
vortex pinning by individual irradiation-induced amorphous columnar defects is
to be expected, vortex motion is limited by the nucleation of vortex kinks at
the specimen surface rather than by half-loop nucleation in the bulk. In the
material bulk, vortex motion occurs through (easy) kink sliding. Depinning in
the bulk determines the screening current only at fields comparable to or
larger than the matching field, at which the majority of moving vortices is not
trapped by an ion track.Comment: 5 pages, 5 figures, submitted to Physical Review Letter
Rubidium in Metal-Deficient Disk and Halo Stars
We report the first extensive study of stellar Rb abundances. High-resolution
spectra have been used to determine, or set upper limits on, the abundances of
this heavy element and the associated elements Y, Zr, and Ba in 44 dwarfs and
giants with metallicities spanning the range -2.0 <[Fe/H] < 0.0. In
metal-deficient stars Rb is systematically overabundant relative to Fe; we find
an average [Rb/Fe] of +0.21 for the 32 stars with [Fe/H] < -0.5 and measured
Rb. This behavior contrasts with that of Y, Zr, and Ba, which, with the
exception of three new CH stars (HD 23439A and B and BD +5 3640), are
consistently slightly deficient relative to Fe in the same stars; excluding the
three CH stars, we find the stars with [Fe/H] < -0.5 have average [Y/Fe],
[Zr/Fe], and [Ba/Fe] of --0.19 (24 stars), --0.12 (28 stars), and --0.06 (29
stars), respectively. The different behavior of Rb on the one hand and Y, Zr,
and Ba on the other can be attributed in part to the fact that in the Sun and
in these stars Rb has a large r-process component while Y, Zr, and Ba are
mostly s-process elements with only small r-process components. In addition,
the Rb s-process abundance is dependent on the neutron density at the
s-processing site. Published observations of Rb in s-process enriched red
giants indicate a higher neutron density in the metal-poor giants. These
observations imply a higher s-process abundance for Rb in metal-poor stars. The
calculated combination of the Rb r-process abundance, as estimated for the
stellar Eu abundances, and the s-process abundance as estimated for red giants
accounts satisfactorily for the observed run of [Rb/Fe] with [Fe/H].Comment: 23 pages, 5 tables, 7 figure
Chaos driven fusion enhancement factor at astrophysical energies
We perform molecular dynamics simulations to assess the screening effects by
bound target electrons in low energy nuclear reactions in laboratories. Quantum
effects corresponding to the Pauli and Heisenberg principle are enforced by
constraints. We show that the enhancement of the average cross section and of
its variance is due to the perturbations induced by the electrons.This gives a
correlation between the maximum amplitudes of the inter-nuclear oscillational
motion and the enhancement factor. It suggests that the chaotic behavior of the
electronic motion affects the magnitude of the enhancement factor.Comment: 4 pages, 3 figure
Tendencias poblacionales recientes de la avutarda hubara en las Islas Canarias: análisis metodológico y estado de conservación
El establecimiento del estatus de conservación demanda la existencia de datos rigurosos y fiables acerca de los efectivos y las tendencias poblacionales, especialmente si se han de aplicar en islas en donde las especies tienen poblaciones pequeñas. Este trabajo analiza la valía de los resultados previos para la hubara utilizando el método de transectos lineales adyacentes separados 200 m, como puntos de partida adecuados para establecer tendencias poblacionales robustas en las 30 localidades principales de las islas de Lanzarote y Fuerteventura. Para ello se efectuaron censos en las mismas fechas (noviembre–diciembre 2011) y localidades estimando la probabilidad de detección. Este método de censo, que estima el máximo número de hubaras diferentes detectadas, proporciona valores de densidad muy poco subestimados (detección del 95,2% de las aves), por lo que las estimas previas de abundancia pueden ser consideradas como fiables (i.e., probable subestima media de un 5%). No obstante, los intervalos de confianza de las estimas de hubaras en las zonas prospectadas mediante un solo censo fueron enormes. Por tanto, con un solo censo por localidad y año no es posible obtener estimas precisas con un escaso margen de variabilidad en torno al valor medio. Esto plantea un problema considerable a la hora de obtener evidencias sólidas acerca de la certeza de los aumentos–disminuciones de los efectivos poblacionales al comparar fechas o zonas diferentes. La avutarda hubara ha disminuido significativamente su densidad de 2004/2006 a 2011 en ocho zonas de Fuerteventura (Vega Vieja, Los Alares–Pocetas, Matas Blancas, Lorenzo–Diviso, Corralejo, Lajares y Fimapaire) y en dos de Lanzarote (Argana y La Santa). Por el contrario, la densidad de la hubara ha aumentado significativamente en tres localidades de Lanzarote (Zonzamas, Guatiza y llano de Las Maretas). Globalmente, las estimas medias por isla no difirieron significativamente entre 2004/2006 y 2011 en Fuerteventura (leve disminución del 29% en 2011), pero sí en Lanzarote (aumento del 60% en 2011). El cambio de densidad entre los dos periodos de estudio tendió al incremento en 2011 en las localidades más alejadas de la carretera asfaltada más cercana, y tendió a la disminución en 2011 en las zonas con suelo predominantemente arenoso.Determining conservation status requires rigorous and reliable data about population sizes and trends, especially if they have to be applied to islands where the species have small populations. The Canary bustard houbara (Chlamydotis undulata fuertaventurae) is catalogued as ‘in danger’ by the Red Book of the Birds of Spain. This work analyzes the value of previously published information on the species using the method of adjacent linear transects separated by 200 m, as a baseline for establishing robust population trends in 30 important areas (ranging from 1.3 to 12.8 km2) for the houbara in the islands of Lanzarote and Fuerteventura (Canary Islands). Censuses were repeated on the same dates (from November to December) and localities as those carried out in 1994, 2004 and 2006. The detection probability of the houbara was estimated by means of distance sampling, being 0.42 up to 250 m from the observer, and 0.82 in the main census belt of 100 m on either side of the line transect. The method of adjacent linear transects —counting the maximum number of hubaras detected— provides accurate figures of population densities (detection of 95.2% of the birds). The previous estimations of houbara densities can therefore be considered highly trustworthy, with a probable average underestimation of only 5 %. Nevertheless, the confidence intervals of density estimations using only one census were very large. Therefore, with only one census per sampling area and year it is not possible to obtain precise estimates of houbara densities with small variation around the average value. This raises concern when trying to obtain solid evidence about the increases–decreases of houbara populations comparing different dates or study areas. The density of the Canary Island hubara bustard decreased significantly from 2004/2006 to 2011 in eight areas of Fuerteventura (Vega Vieja, Los Alares–Pocetas, Matas Blancas, Lorenzo– Diviso, Corralejo, Lajares and Fimapaire) and in two areas of Lanzarote (Argana and La Santa). Conversely, the density of the houbara significantly increased in three areas of Lanzarote (Zonzamas, Guatiza and Llano de las Maretas). As a whole, average population density did not differ significantly between 2004/2006 and 2011 in Fuerteventura (slight decrease of 29% in 2011), but there was a significant increase in Lanzarote (increase of 60% from 2004/2006 to 2011). The change in density from 2004/2006 to 2011 tended to be an increase in areas further from paved roads, and a decrease in locations predominantly covered by loose sandy soils.El establecimiento del estatus de conservación demanda la existencia de datos rigurosos y fiables acerca de los efectivos y las tendencias poblacionales, especialmente si se han de aplicar en islas en donde las especies tienen poblaciones pequeñas. Este trabajo analiza la valía de los resultados previos para la hubara utilizando el método de transectos lineales adyacentes separados 200 m, como puntos de partida adecuados para establecer tendencias poblacionales robustas en las 30 localidades principales de las islas de Lanzarote y Fuerteventura. Para ello se efectuaron censos en las mismas fechas (noviembre–diciembre 2011) y localidades estimando la probabilidad de detección. Este método de censo, que estima el máximo número de hubaras diferentes detectadas, proporciona valores de densidad muy poco subestimados (detección del 95,2% de las aves), por lo que las estimas previas de abundancia pueden ser consideradas como fiables (i.e., probable subestima media de un 5%). No obstante, los intervalos de confianza de las estimas de hubaras en las zonas prospectadas mediante un solo censo fueron enormes. Por tanto, con un solo censo por localidad y año no es posible obtener estimas precisas con un escaso margen de variabilidad en torno al valor medio. Esto plantea un problema considerable a la hora de obtener evidencias sólidas acerca de la certeza de los aumentos–disminuciones de los efectivos poblacionales al comparar fechas o zonas diferentes. La avutarda hubara ha disminuido significativamente su densidad de 2004/2006 a 2011 en ocho zonas de Fuerteventura (Vega Vieja, Los Alares–Pocetas, Matas Blancas, Lorenzo–Diviso, Corralejo, Lajares y Fimapaire) y en dos de Lanzarote (Argana y La Santa). Por el contrario, la densidad de la hubara ha aumentado significativamente en tres localidades de Lanzarote (Zonzamas, Guatiza y llano de Las Maretas). Globalmente, las estimas medias por isla no difirieron significativamente entre 2004/2006 y 2011 en Fuerteventura (leve disminución del 29% en 2011), pero sí en Lanzarote (aumento del 60% en 2011). El cambio de densidad entre los dos periodos de estudio tendió al incremento en 2011 en las localidades más alejadas de la carretera asfaltada más cercana, y tendió a la disminución en 2011 en las zonas con suelo predominantemente arenoso
Spitzer observations of the Orion OB1 association: disk census in the low mass stars
We present new Spitzer Space Telescope observations of two fields in the
Orion OB1 association. We report here IRAC/MIPS observations for 115 confirmed
members and 41 photometric candidates of the ~10 Myr 25 Orionis aggregate in
the OB1a subassociation, and 106 confirmed members and 65 photometric
candidates of the 5 Myr region located in the OB1b subassociation. The 25
Orionis aggregate shows a disk frequency of 6% while the field in the OB1b
subassociation shows a disk frequency of 13%. Combining IRAC, MIPS and 2MASS
photometry we place stars bearing disks in several classes: stars with
optically thick disks (class II systems), stars with an inner transitional
disks (transitional disk candidates) and stars with "evolved disks"; the last
exhibit smaller IRAC/MIPS excesses than class II systems. In all, we identify 1
transitional disk candidate in the 25 Orionis aggregate and 3 in the OB1b
field; this represents ~10% of the disk bearing stars, indicating that the
transitional disk phase can be relatively fast. We find that the frequency of
disks is a function of the stellar mass, suggesting a maximum around stars with
spectral type M0. Comparing the infrared excess in the IRAC bands among several
stellar groups we find that inner disk emission decays with stellar age,
showing a correlation with the respective disk frequencies. The disk emission
at the IRAC and MIPS bands in several stellar groups indicates that disk
dissipation takes place faster in the inner region of the disks. Comparison
with models of irradiated accretion disks, computed with several degrees of
settling, suggests that the decrease in the overall accretion rate observed in
young stellar groups is not sufficient to explain the weak disk emission
observed in the IRAC bands for disk bearing stars with ages 5 Myr or older.Comment: Accepted in the Astrophysical Journa
uvbyCa H beta CCD Photometry of Clusters. VII. The Intermediate-Age Anticenter Cluster Melotte 71
CCD photometry on the intermediate-band uvbyCa H beta system is presented for
the anticenter, intermediate-age open cluster, Melotte 71. Restricting the data
to probable single members of the cluster using the color-magnitude diagram and
the photometric indices alone generates a sample of 48 F dwarfs on the
unevolved main sequence. The average E(b-y) = 0.148 +/- 0.003 (s.e.m.) or
E(B-V) = 0.202 +/- 0.004 (s.e.m.), where the errors refer to internal errors
alone. With this reddening, [Fe/H] is derived from both m1 and hk, using H beta
and b-y as the temperature index, with excellent agreement among the four
approaches and a final weighted average of [Fe/H] = -0.17 +/- 0.02 (s.e.m.) for
the cluster, on a scale where the Hyades has [Fe/H] = +0.12. When adjusted for
the higher reddening estimate, the previous metallicity estimates from
Washington photometry and from spectroscopy are now in agreement with the
intermediate-band result. From comparisons to isochrones of appropriate
metallicity, the cluster age and distance are determined as 0.9 +/- 0.1 Gyr and
(m-M) = 12.2 +/- 0.1 or (m-M)_0 = 11.6 +/- 0.1. At this distance from the sun,
Mel 71 has a galactocentric distance of 10.0 kpc on a scale where the sun is
8.5 kpc from the galactic center. Based upon its age, distance, and elemental
abundances, Mel 71 appears to be a less populous analog to NGC 3960.Comment: Accepted for Astronomical Journal. 38 page latex file includes 11
figures and short version of data table. Full table will appear in online AJ
or may be requested from author
Comparison of embedded and added motor imagery training in patients after stroke: Results of a randomised controlled pilot trial
Copyright @ 2012 Schuster et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Background: Motor imagery (MI) when combined with physiotherapy can offer functional benefits after stroke. Two MI integration strategies exist: added and embedded MI. Both approaches were compared when learning a complex motor task (MT): ‘Going down, laying on the floor, and getting up again’. Methods: Outpatients after first stroke participated in a single-blinded, randomised controlled trial with MI embedded into physiotherapy (EG1), MI added to physiotherapy (EG2), and a control group (CG). All groups participated in six physiotherapy sessions. Primary study outcome was time (sec) to perform the motor task at pre and post-intervention. Secondary outcomes: level of help needed, stages of MT-completion, independence, balance, fear of falling (FOF), MI ability. Data were collected four times: twice during one week baseline phase (BL, T0), following the two week intervention (T1), after a two week follow-up (FU). Analysis of variance was performed. Results: Thirty nine outpatients were included (12 females, age: 63.4 ± 10 years; time since stroke: 3.5 ± 2 years; 29 with an ischemic event). All were able to complete the motor task using the standardised 7-step procedure and reduced FOF at T0, T1, and FU. Times to perform the MT at baseline were 44.2 ± 22s, 64.6 ± 50s, and 118.3 ± 93s for EG1 (N = 13), EG2 (N = 12), and CG (N = 14). All groups showed significant improvement in time to complete the MT (p < 0.001) and degree of help needed to perform the task: minimal assistance to supervision (CG) and independent performance (EG1+2). No between group differences were found. Only EG1 demonstrated changes in MI ability over time with the visual indicator increasing from T0 to T1 and decreasing from T1 to FU. The kinaesthetic indicator increased from T1 to FU. Patients indicated to value the MI training and continued using MI for other difficult-to-perform tasks. Conclusions: Embedded or added MI training combined with physiotherapy seem to be feasible and benefi-cial to learn the MT with emphasis on getting up independently. Based on their baseline level CG had the highest potential to improve outcomes. A patient study with 35 patients per group could give a conclusive answer of a superior MI integration strategy.The research project was partially funded by the Gottfried und Julia Bangerter-Rhyner Foundation
New Low-Mass Stars and Brown Dwarfs with Disks in Lupus
Using the Infrared Array Camera and the Multiband Imaging Photometer aboard
the {\it Spitzer Space Telescope}, we have obtained images of the Lupus 3
star-forming cloud at 3.6, 4.5, 5.8, 8.0, and 24 \micron. We present photometry
in these bands for the 41 previously known members that are within our images.
In addition, we have identified 19 possible new members of the cloud based on
red 3.6-8.0 \micron colors that are indicative of circumstellar disks. We have
performed optical spectroscopy on 6 of these candidates, all of which are
confirmed as young low-mass members of Lupus 3. The spectral types of these new
members range from M4.75 to M8, corresponding to masses of 0.2-0.03
for ages of Myr according to theoretical evolutionary models. We also
present optical spectroscopy of a candidate disk-bearing object in the vicinity
of the Lupus 1 cloud, 2M 1541-3345, which Jayawardhana & Ivanov recently
classified as a young brown dwarf ( ) with a spectral type
of M8. In contrast to their results, we measure an earlier spectral type of
M5.750.25 for this object, indicating that it is probably a low-mass star
( ). In fact, according to its gravity-sensitive absorption
lines and its luminosity, 2M 1541-3345 is older than members of the Lupus
clouds ( Myr) and instead is probably a more evolved
pre-main-sequence star that is not directly related to the current generation
of star formation in Lupus.Comment: 18 pages, 3 tables, 6 figure
- …