Importance of tetrahedral coordination for high-valent transition metal oxides: YCrO4_4 as a model system

We have investigated the electronic structure of the high oxidation state material YCrO$_4$ within the framework of the Zaanen-Sawatzky-Allen phase diagram. While Cr$^{4+}$-based compounds like SrCrO$_3$/CaCrO$_3$ and CrO$_2$ can be classified as small-gap or metallic negative-charge-transfer systems, we find using photoelectron spectroscopy that YCrO$_4$ is a robust insulator despite the fact that its Cr ions have an even higher formal valence state of 5+. We reveal using band structure calculations that the tetrahedral coordination of the Cr$^{5+}$ ions in YCrO$_4$ plays a decisive role, namely to diminish the bonding of the Cr $3d$ states with the top of the O $2p$ valence band. This finding not only explains why the charge-transfer energy remains effectively positive and the material stable, but also opens up a new route to create doped carriers with symmetries different from those of other transition-metal ions.Comment: 6 pages, 6 figure

Tagging Spanish Texts: the Problem of ‘se’

Automatic tagging in Spanish has historically faced many problems because of some specific grammatical constructions. One of these traditional pitfalls is the ‘se’ particle. This particle is a multifunctional and polysemous word used in many different contexts. Many taggers do not distinguish the possible uses of ‘se’ and thus provide poor results at this point. In tune with the philosophy of free software, we have taken a free annotation tool as a basis, we have improved and enhanced its behaviour by adding new rules at different levels and by modifying certain parts in the code to allow for its possible implementation in other EAGLES-compliant tools. In this paper, we present the analysis carried out with different annotators for selecting the tool, the results obtained in all cases as well as the improvements added and the advantages of the modified tagger

The Classification of M1-78

The published properties of M1-78 are discussed with the purpose to resolve the object's classification as either a planetary nebula or an ultracompact HII region. A classification as a planetary nebula is rejected primarily because of the high luminosity of the object, but because of the chemical composition and expansion velocity of the nebula, a novel classification is proposed instead: that of an ultracompact HII region with a post-main sequence central star (possibly a WN star). It must therefore follow that observable ultracompact HII regions persist beyond the main sequence lifetimes of at least some massive stars, and so cannot be transient phenomena that are seen only during pre-main sequence or early main sequence evolution.Comment: 16 pages, Postscrip

Maximal isometric handgrip strength and endurance differences between elite and non-elite young judo athletes

Background and Study Aim: Judo is a combat sport in which the maintenance of handgrip strength is essential because the judokas repeat this action continuously during the struggle for grip. While descriptions of maximal isometric handgrip strength in judokas are relatively common, few data exist concerning the ability to resist successive isometric contractions in the hands and its relation to performance. The aim of this study was the differences and similarities between elite and non-elite young judokas in terms of maximal isometric handgrip strength and their endurance to this strength.Material and Methods: Seventy-three adolescents participants from three national (elite) and one regional team (non-elite) were tested. The maximal isometric handgrip strength was recorded during a maximum test of 6 s with an electronic Digimax dynamometer. The endurance to the isometric handgrip strength was measured by a test consisting of 8 contractions of 10 s each alternating with 10 s of passive rest, and was also recorded with the same machine.Results: The endurance test decreases the relative and mean isometric handgrip strength of male and female judokas (p≤0.01), irrespective of their competitive level. However, male and female elite judokas developed higher levels of relative isometric handgrip strength in the maximum test and during all contractions of the endurance test than non-elite judokas (p≤0.01 for both sexes). In all cases, the non-elite group took longer to reach the maximal isometric handgrip strength (p≤0.05).Conclusions: Maximal isometric handgrip strength and the endurance to this strength were able to distinguish between elite and non-elite young judokas. Coaches should include conditioning programs for both maximal isometric handgrip strength and the ability to resist successive isometric contractions to maximize performance

An eco-physiological and biotechnological approach to conservation of the world-wide rare and endangered aquatic liverwort Riella helicophylla (Bory et Mont.) Mont.

The rare aquatic liverwort Riella helicophylla (Bory et Mont.) Mont., inhabitant of temporary shallow ponds around the Mediterranean basin, is considered threatened throughout its distribution range. In addition, little is known of its biology and ecology or of its role in such an important ecosystem where envi- ronmental conditions vary yearly in unpredictable ways. In these variable habitats, due to the seasonal fluc- tuation of water levels, there is no guarantee of yearly spore input into the spore bank. Spore germination rate and the effects of different culture media in an axenic culture establishment, as well as propagation proce- dures of R. helicophylla, were tested. New insights into the ecology and biology of R. helicophylla are given. Spore dormancy is documented, and the protocols for the in vitro culture establishment, propagation and ac- climatization of this liverwort are developed. Dry storage at 20 ± 2 °C for about three months broke the dor- mancy of spores, which subsequently germinated in a high percentage (over 90%). A two phase (solid and liquid) culture media system was developed for the purpose of achieving fully developed gametophytes. The liquid phase contained electrolytes simulating brackish water

Recent Star Formation in Sextans A

We investigate the relationship between the spatial distributions of stellar populations and of neutral and ionized gas in the Local Group dwarf irregular galaxy Sextans A. This galaxy is currently experiencing a burst of localized star formation, the trigger of which is unknown. We have resolved various populations of stars via deep UBV(RI)_C imaging over an area with diameter \sim 5.'3. We have compared our photometry with theoretical isochrones appropriate for Sextans A, in order to determine the ages of these populations. We have mapped out the history of star formation, most accurately for times \lesssim 100 Myr. We find that star formation in Sextans A is correlated both in time and space, especially for the most recent (\lesssim 12 Myr) times. The youngest stars in the galaxy are forming primarily along the inner edge of the large H I shell. Somewhat older populations, \lesssim 50 Myr, are found inward of the youngest stars. Progressively older star formation, from \sim 50--100 Myr, appears to have some spatially coherent structure and is more centrally concentrated. The oldest stars we can accurately sample appear to have approximately a uniform spatial distribution, which extends beyond a surface brightness of \mu_B \simeq 25.9 mag arcsec^{-2} (or, a radius r \simeq 2.'3$). Although other processes are also possible, our data provides support for a mechanism of supernova-driven expansion of the neutral gas, resulting in cold gas pileup and compression along the H I shell and sequential star formation in recent times.Comment: 64 pages, 22 figures, to appear in A

Inhomogeneous electronic structure probed by spin-echo experiments in the electron doped high-Tc superconductor Pr_{1.85}Ce_{0.15}CuO_{4-y}

63Cu nuclear magnetic resonance (NMR) spin-echo decay rate (T_2^{-1}) measurements are reported for the normal and superconducting states of a single crystal of Pr_{1.85}Ce_{0.15}CuO_{4-y} (PCCO) in a magnetic field B_0=9T over the temperature range 2K<T<200K. The spin-echo decay rate is temperature-dependent for T<55K, and has a substantial dependence on the radio frequency (rf) pulse parameters below T~25K. This dependence indicates that T_2^{-1} is strongly effected by a local magnetic field distribution that can be modified by the rf pulses, including ones that are not at the nuclear Larmor frequency. The low-temperature results are consistent with the formation of a static inhomogeneous electronic structure that couples to the rf fields of the pulses.Comment: 4 pages, 4 figure

Extra-planar gas in the spiral galaxy NGC 4559

We present 21-cm line observations of the spiral galaxy NGC 4559, made with the Westerbork Synthesis Radio Telescope. We have used them to study the HI distribution and kinematics, the relative amount and distribution of luminous and dark matter in this galaxy and, in particular, the presence of extra-planar gas. Our data do reveal the presence of such a component, in the form of a thick disk, with a mass of 5.9 x 10^8 Mo (one tenth of the total HI mass) and a mean rotation velocity 25-50 km/s lower than that of the thin disk. The extra-planar gas may be the result of galactic fountains but accretion from the IGM cannot be ruled out. With this study we confirm that lagging, thick HI layers are likely to be common in spiral galaxies.Comment: 17 pages, 10 figures. Accepted for publication in A&