NEW PHYTOTRON FOR STUDYING THE EFFECT OF CLIMATE CHANGE ON PLANT PATHOGENS

The Intergovernmental Panel on Climate Change in its recent fourth assessment report predicts that, because of higher concentrations of greenhouse gases in the atmosphere, until 2100 the global mean temperature would rise between 0.6 and 4°C, in combination with changes in precipitation and an increased frequency of extreme weather events. Despite this trend, the extent and mechanisms through which elevated CO2 affects plant diseases remain uncertain. Increases in CO2 and temperatures are also expected to induce complex effects on plant pathogens. Although re- 10 search on the effects of climate change continues to be limited, new tools are permitting to study the effects of climate variables on infection rates in the case of some pathosystems. The shortage of critical epidemiological data on individual plant diseases needs to be addressed using experimental approaches. A useful tool for such types of studies is represented by phytotrons. Hereby, a new phytotron typology, built with the specific aim of studying the effect of climate change on plant disease, is described. Beginning from a general plant overview, key mechanical and electrical systems are described (i.e. air temperature and relative humidity control, lighting and CO2 control system etc.) as environmental parameters and operation cycle are summarized. In particular both parameters which could be set and monitored and those measured and stored are reported. After a suitable testing period, several operation cycles were performed in order to assess the control system's stability and to optimize the management of all systems involved and the first experimental trials were carried out. The effect of three different simulated climatic conditions: 450 ppm of CO2 with standard temperature (ranging from 18 to 24°C or 18 to 26°C), elevated CO2 (800 ppm) with standard temperature and elevated CO2 (800 ppm) with elevated temperature (4°C higher than standard) on the development of grape powdery and downy mildew were tested

Effet tunnel dans les systèmes magnétiques : de la description microscopique et déterministe à l'équation maîtresse

Spin relaxation in a solid depends sometimes on tunneling between two excited crystal field states $|a\rangle$ and $|b\rangle$. The calculation of the tunneling frequency $\omega_{ab}$ at resonance in the absence of damping is a classical problem. In the presence of damping, one can deduce the relaxation time from master equations in which tunneling appears through the transition probability $\Gamma_{ab}$ between $|a\rangle$ and $|b\rangle$. We derive the result $\Gamma_{ab}=2\omega^2_{ab}\tau_{ab}/[1+\tau_{ab}^2(E_a - E_b)^2/\hbar^2]$, where $E_a -E_b$ is a linear function of the magnetic field, $\tau_{ab}=\tau_a\tau_b/(\tau_a+\tau_b)$ and $\tau_a$ and $\tau_b$ are the respective lifetimes of $|a\rangle$ and $|b\rangle$ which depend on the spin-phonon interaction and can be calculated in the absence of tunneling. A mechanical analogy provides an intuitive picture of the phenomenon. The master equations are identical to the equations which describe the discharge of condensators through an electric network.La relaxation d'un spin dans un solide dépend dans certains cas de l'effet tunnel entre deux états de champ cristallin excités $|a\rangle$ et $|b\rangle$. Le calcul de la fréquence tunnel $\omega_{ab}$ à la résonance est un problème classique en l'absence d'amortissement. En présence d'amortissement, on peut déduire le temps de relaxation d'une équation maîtresse où l'effet tunnel est modélisé par une probabilité de transition $\Gamma_{ab}$ entre $|a\rangle$ et $|b\rangle$. Nous démontrons la formule $\Gamma_{ab}=2\omega_{ab}^2\tau_{ab}/[1+\tau_{ab}^2(E_a - E_b)^2/\hbar^2]$, où $E_a -E_b$ est une fonction linéaire du champ magnétique, $\tau_{ab}=\tau_a\tau_b/(\tau_a+\tau_b)$, enfin $\tau_a$ et $\tau_b$ sont les temps de vie de $|a\rangle$ et $|b\rangle$, qui dépendent de l'interaction spin-phonon et peuvent être calculés en l'absence d'effet tunnel. On propose une analogie mécamique qui donne une image intuitive du phénomène. Les équations maîtresses sont identiques à celles qui décrivent la décharge de condensateurs dans un réseau électrique

Strongly hybridized dipole-exchange spin waves in thin Fe-N ferromagnetic films

International audienc

Stripe domains reorientation in ferromagnetic films with perpendicular magnetic anisotropy

International audienceFerromagnetic thin films with moderate perpendicular magnetic anisotropy (PMA) are known to support weak stripe domains provided film thickness exceeds a critical value. In this work, we performed both an experimental and theoretical investigation of a peculiar phenomenon shown by weak stripe domains: namely, the stripe domains reorientation when a dc magnetic field is applied in the film plane along the direction perpendicular to the stripes axis. We focus on bct α ′-Fe 8 N 1−x thin films obtained by N 2 irradiation of α-Fe films epitaxially grown on ZnSe/ GaAs(001). By using different ion implantation and heat treatment conditions, we show that it is possible to tune the PMA values. Magnetic force microscopy and vibrating sample magnetometer measurements prove the existence of weak stripe domains at remanence, and of a threshold field for the reorientation of the stripes axis in a transversal field. Using a one-dimensional model of the magnetic stripe domains, where the essential parameter is the maximum canting angle of the stripe magnetization out of the film plane, the various contributions to the magnetic energy can be separately calculated. A linear increase of the reorientation threshold field Stripe domains reorientation in ferromagnetic films with PMA 2 on the PMA is obtained, in qualitative agreement with experimental data in our Fe-N films, as well as in other thin films with weak stripe domains. Finally, we find that also the rotatable anisotropy field linearly increases as a function of the PMA magnitude

The Food Standards Agency A force for change

Presented to Parliament by the Minister of Agriculture, Fisheries and Food by command of Her MajestyAvailable from British Library Document Supply Centre-DSC:OP-CM/3830 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo