National University of La Plata

About: National University of La Plata is a education organization based out in La Plata, Argentina. It is known for research contribution in the topics: Population & Stars. The organization has 12993 authors who have published 30013 publications receiving 495118 citations. The organization is also known as: UNLP & Universidad Nacional de La Plata.

Comparison of in vitro solubilization activity of diverse phosphate-solubilizing bacteria native to acid soil and their ability to promote Phaseolus vulgaris growth

Abstract: To identify plant growth promotion ability of phosphorus-solubilizing native bacteria, we have examined a collection of isolates representing the diversity of culturable phosphate-solubilizing bacteria from acid soils of the northeast of Argentina. Assays in growth medium supplemented with tricalcium phosphate revealed different phosphorus solubilization activity and temporal patterns of solubilization. Acidification of the broth medium coincided with phosphorus solubilization. The isolates were grouped according to their Rep fingerprinting profiles and phylogenetically classified by 16S rDNA and biochemical analyses. These isolates were assigned to the genera Enterobacter, Pantoea, Pseudomonas, Acinetobacter, Burkholderia, and Exiguobacterium. Four isolates showing high phosphorus solubilizing activity in in vitro assays were inoculated on common beans (Phaseolus vulgaris); some of them promoted plant growth and increased photosynthesis and the P and N content of leaves. The results indicated that the ability to in vitro solubilize P is not necessarily associated to the promotion of plant growth.

New evolutionary sequences for extremely low-mass white dwarfs - Homogeneous mass and age determinations and asteroseismic prospects

Abstract: Context. The number of detected extremely low-mass (ELM) white dwarf stars has increased drastically in recent years, thanks to the results of many surveys. In addition, some of these stars have been found to exhibit pulsations, making them potential targets for asteroseismology.Aims. We provide a fine and homogeneous grid of evolutionary sequences for helium (He) core white dwarfs for the whole range of their expected masses (0.15 ≲ M ∗ /M ⊙ ≲ 0.45), including the mass range for ELM white dwarfs (M ∗ /M ⊙ ≲ 0.20). The grid is appropriate for mass and age determination of these stars, as well as for studying their adiatabic pulsational properties.Methods. White dwarf sequences have been computed by performing full evolutionary calculations that consider the main energy sources and processes of chemical abundance changes during white dwarf evolution. Realistic initial models for the evolving white dwarfs have been obtained by computing the nonconservative evolution of a binary system consisting of an initially 1 M ⊙ ZAMS star and a 1.4 M ⊙ neutron star for various initial orbital periods. To derive cooling ages and masses for He-core white dwarfs, we perform a least square fitting of the M (T eff ,g ) and Age(T eff ,g ) relations provided by our sequences by using a scheme that takes into account the time spent by models in different regions of the T eff − g plane. This is particularly useful when multiple solutions for cooling age and mass determinations are possible in the case of CNO-flashing sequences. We also explore in a preliminary way the adiabatic pulsational properties of models near the critical mass for the development of CNO flashes (~0.2 M ⊙ ). This is motivated by the discovery of pulsating white dwarfs with stellar masses near this threshold value. Results. We obtain reliable and homogeneous mass and cooling age determinations for 58 very low-mass white dwarfs, including three pulsating stars. Also, we find substantial differences in the period spacing distributions of g -modes for models with stellar masses near ~ 0.2 M ⊙ , which could be used as a seismic tool to distinguish stars that have undergone CNO flashes in their early cooling phase from those that have not. Finally, for an easy application of our results, we provide a reduced grid of values useful to obtain the masses and ages of He-core white dwarfs.

Testing Hadronic Interactions at Ultrahigh Energies with Air Showers Measured by the Pierre Auger Observatory.

Abstract: Ultrahigh energy cosmic ray air showers probe particle physics at energies beyond the reach of accelerators Here we introduce a new method to test hadronic interaction models without relying on the absolute energy calibration, and apply it to events with primary energy 6-16 EeV (E_CM = 110-170 TeV), whose longitudinal development and lateral distribution were simultaneously measured by the Pierre Auger Observatory The average hadronic shower is 133 +- 016 (161 +- 021) times larger than predicted using the leading LHC-tuned models EPOS-LHC (QGSJetII-04), with a corresponding excess of muons