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.

Deep tillage and traffic effects on subsoil compaction and sunflower (Helianthus annus L.) yields

Abstract: The main function of deep tillage is to alleviate subsoil compaction, but how long do the benefits of this technique remain? Traffic on loose soil causes a significant increase in soil compaction. Subsoiling and chisel plowing were carried out at 450 and 280 mm depth, respectively on a compacted soil in the west Rolling Pampas region of Argentina. The draft required, physical soil properties, root growth, sunflower ( Helianthus annus L. Merr.) yield and traffic compaction over the subsequent two growing seasons were measured. Cone penetrometer resistance was reduced and sunflower yields increased following deep tillage operations. Subsoil compaction caused changes to the root system of sunflower that affected shoot growth and crop yields. Although subsoiling and chiseling had an immediate loosening effect, it was evident that after just 2 years, when traffic intensity was >95 mg km ha −1 , re-compaction and settling had occurred in the 300–600 mm depth range.

Effect of ethylene and 1-MCP treatments on strawberry fruit ripening.

Abstract: BACKGROUND: Strawberry is a soft fruit, considered as non-climacteric, being auxins the main hormones that regulate the ripening process. The role of ethylene in strawberry ripening is currently unclear and several studies have considered a revision of the possible role of this hormone. RESULTS: Strawberry fruit were harvested at the white stage and treated with ethephon, an ethylene-releasing reagent, or 1-methylcyclopropene (1-MCP), a competitive inhibitor of ethylene action. The effects of the treatments on fruit quality parameters and on the activity of enzymes related to anthocyanin synthesis and cell wall degradation were evaluated. Some aspects of ripening were accelerated (anthocyanin accumulation, total sugar content and increment of phenylalanine ammonia-lyase (PAL; EC 4.3.1.24) and β-galactosidase (EC 3.2.1.23) activities), while others were repressed (chlorophyll levels and increment of endo-1,4-β-glucanase (EC 3.2.1.4) and β-xylosidase (EC 3.2.1.37) activities) or unchanged (reducing sugar content, pH, titratable acidity and α-L-arabinofuranosidase (EC 3.2.1.55) activity) by ethylene. 1-MCP treatment caused the opposite effect. However, its effects were more pronounced, particularly in anthocyanin accumulation, phenolics, PAL and polygalacturonase (EC 3.2.1.15 and EC 3.2.1.67) activities. CONCLUSION: These observations probably indicate that strawberry produces low levels of ethylene that are sufficient to regulate some ripening aspects. Copyright © 2010 Society of Chemical Industry

Further Insights into the Structure of 30 Doradus from the Hubble Space Telescope Instruments

Abstract: New observations with the Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2), combined with prior archival data, provide nearly complete coverage of the inner 30 Doradus Nebula in both nebular lines and continuum at 01 resolution The developing windblown cavity surrounding the massive first-generation, central cluster and its interface with the remanent molecular clouds, the site of second-generation, triggered star formation, are imaged in their entirety Dithered Planetary Camera observations with 003 resolution of Knots 1–3 reveal further structural details of the large dust pillars oriented toward the central cluster and the newborn, massive multiple systems of the second generation in those fields The new data also provide the first WFPC2 coverage of the fields of two interesting, luminous infrared sources observed in our previous Near Infrared Camera and Multi-Object Spectrometer program; comparisons of the high-resolution optical and IR images are illuminating In addition, we have obtained Space Telescope Imaging Spectrograph optical, long-slit observations of seven O-type multiple systems in the region, including those in Knots 1–3 and four representatives of the older generation The spatially resolved spectrograms and classifications of the close pairs, with separations ranging from 009 to 118, are presented, as well as WFPC2 photometry of the individual components and the compact clusters of fainter stars associated with them These new observations, and planned further analysis of them, offer significant new information about the intricate structure and evolution of the two-stage starburst in 30 Dor

Grids of white dwarf evolutionary models with masses from M=0.1 to 1.2 m⊙

Abstract: We present detailed evolutionary calculations for carbon--oxygen- and helium-core white dwarf models with masses ranging from M= 0.1 to 1.2 M⊙ and for metallicities Z = 0.001 and 0. The sequences cover a wide range of hydrogen envelopes as well. We have taken finite-temperature effects fully into account by means of a detailed white dwarf evolutionary code, in which updated radiative opacities and equations of state for hydrogen and helium plasmas are considered. The energy transport by convection is treated within the formalism of the full-spectrum turbulence theory, as given by the self-consistent model of Canuto, Goldman & Mazzitelli. Convective mixing, crystallization, hydrogen burning and neutrino energy losses are taken into account as well. The set of models presented here is very detailed and should be valuable, particularly for the interpretation of observational data on low-mass white dwarfs recently discovered in numerous binary configurations, and also for the general problem of determining the theoretical luminosity function for white dwarfs. In this context, we compare our cooling sequences with the observed white dwarf luminosity function recently improved by Leggett, Ruiz & Bergeron and we obtain an age for the Galactic disc of ≈ 8 Gyr. Finally, we apply the results of this paper to derive stellar masses of a sample of low-mass white dwarfs.

Tsallis entropy and Jaynes' Information Theory formalism

Abstract: The role of Tsalli's non-extensive Information Measure within an a la Jaynes Information-Theory-based formulation of Statistical Mechanics is discussed in rather detailed fashion.