Variability in Tolerance to Water Stress by \u3cem\u3eHolcus Lanatus\u3c/em\u3e L., \u3cem\u3eBromus Valdivianus\u3c/em\u3e Phil. and \u3cem\u3eAgrostis Capillaris\u3c/em\u3e L. Accessions

Holcus lanatus L. (Hl), Bromus valdivianus Phil. (Bv) and Agrostis capillaris L. (Ac) are frequently present in the naturalised pasture of the Chilean humid region, which has a summer drought with two distinguishable areas according to average summer rainfall: a Northern area (Long summer drought, LSuD: 136-186 mm;) and a Southern area (Short summer drought, SSuD: 186-338 mm). It was hypothesised that plant species have colonised areas with different water deficits during summer through differentiated drought tolerance, which would imply ecotype generation

Deriving the respiratory sinus arrhythmia from the heartbeat time series using Empirical Mode Decomposition

Heart rate variability (HRV) is a well-known phenomenon whose characteristics are of great clinical relevance in pathophysiologic investigations. In particular, respiration is a powerful modulator of HRV contributing to the oscillations at highest frequency. Like almost all natural phenomena, HRV is the result of many nonlinearly interacting processes; therefore any linear analysis has the potential risk of underestimating, or even missing, a great amount of information content. Recently the technique of Empirical Mode Decomposition (EMD) has been proposed as a new tool for the analysis of nonlinear and nonstationary data. We applied EMD analysis to decompose the heartbeat intervals series, derived from one electrocardiographic (ECG) signal of 13 subjects, into their components in order to identify the modes associated with breathing. After each decomposition the mode showing the highest frequency and the corresponding respiratory signal were Hilbert transformed and the instantaneous phases extracted were then compared. The results obtained indicate a synchronization of order 1:1 between the two series proving the existence of phase and frequency coupling between the component associated with breathing and the respiratory signal itself in all subjects.Comment: 12 pages, 6 figures. Will be published on "Chaos, Solitons and Fractals

Giant spin-dependent photo-conductivity in GaAsN dilute nitride semiconductor

A theoretical and experimental study of the spin-dependent photoconductivity in dilute Nitride GaAsN is presented. The non linear transport model we develop here is based on the rate equations for electrons, holes, deep paramagnetic and non paramagnetic centers both under CW and pulsed optical excitation. Emphasis is given to the effect of the competition between paramagnetic centers and non paramagnetic centers which allows us to reproduce the measured characteristics of the spin-dependent recombination power dependence. Particular attention is paid to the role of an external magnetic field in Voigt geometry. The photoconductivity exhibits a Hanle-type curve whereas the spin polarization of electrons shows two superimposed Lorentzian curves with different widths, respectively related to the recombination of free and trapped electrons. The model is capable of reproducing qualitatively and quantitatively the most important features of photoluminescence and photocurrent experiments and is helpful in providing insight on the various mechanisms involved in the electron spin polarization and filtering in GaAsN semiconductors.Comment: 10 pages, 5 figure

Exciton dynamics in WSe2 bilayers

We investigate exciton dynamics in 2H-WSe2 bilayers in time-resolved photoluminescence (PL) spectroscopy. Fast PL emission times are recorded for both the direct exciton with $\tau_{D}$ ~ 3 ps and the indirect optical transition with $\tau_{i}$ ~ 25 ps. For temperatures between 4 to 150 K $\tau_{i}$ remains constant. Following polarized laser excitation, we observe for the direct exciton transition at the K point of the Brillouin zone efficient optical orientation and alignment during the short emission time $\tau_{D}$. The evolution of the direct exciton polarization and intensity as a function of excitation laser energy is monitored in PL excitation (PLE) experiments.Comment: 4 pages, 3 figure

Phyllochron and Growth Dynamic of \u3cem\u3eLolium perenne\u3c/em\u3e L. and \u3cem\u3eBromus valdivianus\u3c/em\u3e Phil. as Affected by Soil pH, Phosphorus and Nitrogen Restriction

Permanent grasslands are the main food for livestock production systems in Southern Chile. Therefore, it is essential to develop management tools that optimize the use of pastures. Among these tools, the phyllochron could be a better method to control grazing frequency. The aim of this study was to determine the effect of three levels of soil pH, phosphorus (P) and nitrogen (N) on the phyllochron and growth dynamic of Lolium perenne and Bromus valdivianus. Nine monophytic mini-swards of each species were established in 125 L containers for three different pH, P and N levels. For one year we measured: phyllochron, total leaf length, leaf expansion rate, sheath length, leaf lifespan, number of leaves per tiller, leaf area, radiation interception, biomass production and nutritive value. For each factor, a complete randomized block design with three blocks and a factorial arrangement of two pasture species and three levels was used. Results showed that soil pH, P and N level did not affect the phyllochron on both species, but significantly modified the growth dynamic and nutritive value of them. The non-limited treatment had the highest leaf elongation rate and size, sheath length, leaf area and biomass production. The radiation intercepted was positively correlated to the leaf area, being the highest at the non-limited treatment. The number of leaves per tiller and the leaf lifespan were not modified, since these characteristics are specific to each species

Room temperature Giant Spin-dependent Photoconductivity in dilute nitride semiconductors

By combining optical spin injection techniques with transport spectroscopy tools, we demonstrate a spin-photodetector allowing for the electrical measurement and active filtering of conduction band electron spin at room temperature in a non-magnetic GaAsN semiconductor structure. By switching the polarization of the incident light from linear to circular, we observe a Giant Spin-dependent Photoconductivity (GSP) reaching up to 40 % without the need of an external magnetic field. We show that the GSP is due to a very efficient spin filtering effect of conduction band electrons on Nitrogen-induced Ga self-interstitial deep paramagnetic centers.Comment: 4 pages, 3 figure

Carbohydrate to Protein Ratio in Perennial Ryegrass: Effects of Defoliation Stage and Nitrogen Rate

In intensive grass-based systems, perennial ryegrass (Lolium perenne L) grazed at early stages has a high crude protein content (CP) and low water soluble carbohydrate (WSC) relative to animal requirements. This imbalance leads to low nitrogen (N) use efficiency and a large loss of N excreted to the environment (Dijkstra et al. 2011). Previous research has shown the importance of the WSC:PC ratio as a useful factor that determines the improvement of the animal’s performance in terms of nitrogen utilization (Cosgrove et al. 2007). However, little is known about how the management of defoliation at specific growth stages can modify the WSC:CP ratio and other nutritive parameters related to N use efficiency. The objective of this study was to determine the changes of WSC:CP ratio and other nutritive parameters related to N use efficiency in response to nitrogen fertilizer rate and defoliation frequency based on leaf stage

Impacts of Livestock Preference and Frequency of Grazing on Production and Nutritive Value of Pastures in Chile

Cattle are selective grazers since they only consume some plants or some parts of a plant from the pasture and avoid others. Grazing preference is affected by characteristics of the pasture such as the botanical composition, pasture surface height, herbage mass, phenological stage, digestibility, fibre content, protein and ash content. Three studies were conducted in southern Chile to determine how: 1) grazing preferences of dairy cattle was influenced by pasture mixtures and fertilisation; 2) grazing selectivity was related to tiller features; and 3) grazing leaf-stage influenced pasture quantity and quality. For the first study, fertilised pastures had higher herbage mass, pasture height, Bromus valdivianus, metabolisable energy and crude protein content and had lower fibre content. Grazing time (GT) and bite number (BN) were positively related to metabolisable energy, crude protein content, pre-grazing herbage mass and pasture surface height, explained by the contribution of Lolium perenne and B. valdivianus. For the second study, selective grazing was enhanced by pasture heterogeneity and tiller volume may have favoured grazing probability at a similar nutritive value. For the third study, pastures grazed at a 2.5 leaf-stage yielded a higher herbage mass than those grazed at 1.5 leaf-stage, while increasing leaf-stage decreased pasture quality. Integration of the information on grazing preference and selectivity, and grazing frequency will help to refine grazing management for southern Chile