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.

Drought and watering-dependent oxidative stress: effect on antioxidant content in Triticum aestivum L. leaves

Abstract: The purpose of the present work was to evaluate both oxidative stress and the antioxidant response system in leaves from wheat (Triticum aestivum cv. Buck Poncho) subjected sequentially to drought and watering. Drought was imposed by withholding water until soil water potential reached - 2.0 MPa and maintained under those conditions for 24 h. DCFDA oxidation by wheat leaves was not significantly affected by drought, but watering led to an approximately 2-fold increase in DCFDA oxidation rate. However, no significant effect either on lipid radical content or on hydroperoxide content was measured after drought and drought followed by watering. Microsomes isolated from leaves exposed to drought, and from leaves exposed to drought followed by watering, generated a significantly higher amount of hydroxyl radical as compared to microsomes isolated from control leaves, suggesting a higher production of hydroxyl radical in the cellular water-soluble phase, after drought and watering as compared to control values. The content of α-tocopherol in wheat leaves was increased 2.4-fold after drought and β-carotene content was increased by 2.6-fold after drought. Hydration lowered lipid-soluble antioxidant content to control values. Total thiol content was increased by 70% after drought, and watering did not significantly alter the enhanced values. Drought decreased by 28.5% the content of reduced ascorbic acid. Taken as a whole, active species formed at wheat membranes after exposure to moderate water stress, are efficiently removed upon rehydration by reaction with an increased content of α-tocopherol and β-carotene. Moreover, a co-ordinated response involving glutathione reductase activity, thiols and ascorbic acid is triggered to limit free radical dependent effects.

Size dependence of refractive index of gold nanoparticles

Abstract: The extinction spectra of spherical gold nanoparticles suspended in a homogeneous media were measured and the results were adjusted with Mie's theory together with an appropriate modification of the optical properties of bulk material considering the limitation that introduces the size of nanoparticles on the dielectric function. Usually, the contribution of free electrons to the dielectric function is modified for particle size, while the contribution of bound electrons is assumed to be independent of size. This work discusses the separated contribution of free and bound electrons on the optical properties of particles and their variation with size for gold nanoparticles. The effects of dielectric function and its changes with size on extinction spectra near plasmon resonance are considered. The damping constant for free electrons was changed with size as usual and a scattering constant of C = 0.8 was used. For the bound electron contribution, two different models were analysed to fit the extinction spectra: on the one hand, the damping constant for interband transitions and the gap energy were used as fitting parameters and on the other, the electronic density of states in the conduction band was made size-dependent. For the first model, extinction spectra corresponding to particles with radius R = 0.7 nm were fitted using two sets of values of the energy gap and damping constant: Eg = 2.3 eV and or Eg = 2.1 eV and . For the second model, a simple assumption for the electronic density of states and its contribution to the dielectric function in terms of size allowed to adjust extinction spectra for all samples explored (from 0.3 to 1.6 nm radius). This last model uses only one parameter, a scale factor R0 = 0.35 nm, that controls the contribution of the bound electrons in nanoparticles. Contrast between the maximum and the minimum in the extinction spectra near the resonance at 520 nm or alternatively the broadening of the plasmon band can be used to determine the size of gold nanoparticles with radius smaller than 2 nm.

Muons in air showers at the Pierre Auger Observatory: Mean number in highly inclined events

Abstract: We present the first hybrid measurement of the average muon number in air showers at ultrahigh energies, initiated by cosmic rays with zenith angles between 62° and 80°. The measurement is based on 174 hybrid events recorded simultaneously with the surface detector array and the fluorescence detector of the Pierre Auger Observatory. The muon number for each shower is derived by scaling a simulated reference profile of the lateral muon density distribution at the ground until it fits the data. A 1019eV shower with a zenith angle of 67°, which arrives at the surface detector array at an altitude of 1450 m above sea level, contains on average (2.68±0.04±0.48(sys))×107 muons with energies larger than 0.3 GeV. The logarithmic gain dlnNμ/dlnE of muons with increasing energy between 4×1018eV and 5×1019eV is measured to be (1.029±0.024±0.030(sys)).

Observation and measurement of Higgs boson decays to WW$^*$ with the ATLAS detector

Abstract: We report the observation of Higgs boson decays to $WW^{\ast}$ based on an excess over background of 6.1 standard deviations in the dilepton final state, where the Standard Model expectation is 5.8 standard deviations. Evidence for the vector-boson fusion (VBF) production process is obtained with a significance of 3.2 standard deviations. The results are obtained from a data sample corresponding to an integrated luminosity of $25 \textrm{pb}^{-1}$ from $\sqrt{s}=7$ and 8 TeV $pp$ collisions recorded by the ATLAS detector at the LHC. For a Higgs boson mass of 125.36 GeV, the ratio of the measured value to the expected value of the total production cross section times branching fraction is $1.09^{+0.16}_{-0.15} \textrm{(stat.)}^{+0.17}_{-0.14} \textrm{(syst.)}$. The corresponding ratios for the gluon fusion and vector-boson fusion production mechanisms are $1.02\pm 0.19 \textrm{(stat.)}^{+0.22}_{-0.18} \textrm{(syst.)}$ and $1.27^{+0.44}_{-0.40} \textrm{(stat.)}^{+0.30}_{-0.21} \textrm{(syst.)}$, respectively. At $\sqrt{s}=8$ TeV, the total production cross sections are measured to be $\sigma(gg\to H\rightarrow WW^\ast) = 4.6\pm0.9\,\textrm{(stat.)}\,^{+0.8}_{-0.7}\,\textrm{(syst.)}\textrm{pb}$ and $\sigma(\textrm{VBF} H\rightarrow WW^\ast) = 0.51\,^{+0.17}_{-0.15}\,\textrm{(stat.)}\,^{+0.13}_{-0.08}\,\textrm{(syst.)}\textrm{pb}$. The fiducial cross section is determined for the gluon-fusion process in exclusive final states with zero or one associated jet.

The master algorithm: how the quest for the ultimate learning machine will remake our world

Abstract: Nowadays, “machine learning” is present in several aspects of the current world, internet advisors, advertisements and “smart” devices that seem to know what we need in a given moment. These are some examples of the problems solved by machine learning. This book presents the past, the present and the future of the different types of machine learning algorithms. At the beginning of the book, the author takes us to the first years of the computing science, where a programmer had to do absolutely everything by himself to make an algorithm do a certain task. As time passes, there appeared the first algorithms that were capable of programming themselves learning from the available data. The author presents what he himself calls the five “tribes” of machine learning, the essence that defends each one and the kind of problems that are able to solve without problems. With a great amount of simple examples, the author depicts which advantages and disadvantages of the “master” algorithms of each “tribes” are, saying that the problem that a tribe solves perfectly well, another one cannot do it, and the other way about. The author suggests to get the best out of each “tribe” and make a unique learning algorithm able to learn without caring about the problem: the master algorithm.