The temporary effect of weed-cover maintenance on transpiration and carbon assimilation of olive trees

The maintenance of spontaneous weed cover is a conservation practice used in olive groves. Herbaceous plants in alleys between the trees can increase the capacity of this agroecosystem to remove carbon. However, the influence of this practice on carbon assimilation at the leaf scale has not yet been studied in olive trees. Also, the presence of other species competing with olive trees for soil water has the potential to modify the water use efficiency, a key parameter in a climate change context. In this study, leaf-scale net carbon assimilation (Aleaf), transpiration (Eleaf) and water use efficiency as the ratio Aleaf/Eleaf(WUEleaf) were quantified in olive grove divided by two different treatments: (1) a weed-free (WF) ecosystem in which weed growth was inhibited by applying herbicide; and (2) a weed-covered (WC) ecosystem in which spontaneous herbaceous plants were kept and then mechanically mowed and left on the ground. A portable leaf photosynthesis system was used to measure olive leaf fluxes for both treatments, and likewise for the ecosystem scale via two eddy covariance towers assessing gross primary production (GPPeco), evapotranspiration (ETeco), and water use efficiency (WUEeco). We found that the average Aleaf was 24% higher in the WF treatment while GPPeco decreased 32% compared to WC treatment. However, Aleaf was significantly different between treatments only during weed growth: January-May (Aleaf-WF = 7.6±3.7 μmol CO2m−2s−1; Aleaf-WC = 5.1±3.1 μmol CO2m−2s−1) while Aleaf was similar between the two treatments after mowing. Mowed weeds decreased Tsoil and VPD, and these changes were accompanied by a decrease in Eleaf in olive trees. Therefore, this led to WUEleaf-WF>WUEleaf-WC when the weeds were growing and the opposite after mowing. Thus, although the presence of spontaneous weeds increased the annual ecosystem C uptake in the olive orchard, both Aleaf and seasonal fluctuations in WUEleaf were reduced with weed maintenance

Time-varying thermal dynamics modeling of the prototype of the REMS wind sensor

The objective of this work is to show the results from the analysis of the thermal dynamics of a prototype of the REMS 3D wind anemometer using the tools of Diffusive Representation (DR). DR is a mathematical tool that allows the description of physical phenomena based on diffusion using state- space models of arbitrary order in the frequency domain. From open-loop experimental measurements, where a current signal with a wide frequency spectrum is injected in the heaters, time-varying dynamical thermal models are extracted for different wind velocities. This models provide the temperature evolution of the parts of the system under study as a function of the power delivered to the heat sources. The prototype of the wind sensor used in the experimental setup is based on thermal anemometry, which is the method that has been used in multiple occasions for the challenging task of wind sensing in Mars. It is based on the detection of the wind velocity by measuring the power dissipated of a heated element due to forced convection. This technique was employed in the wind sensor of REMS (Remote Environmental Monitor System) sensor suite, on board Curiosity rover since 2012. In 2018, it is expected to be launched the InSight (Interior Exploration using Seismic Investigation, Geodesy and Heat Transport) mission to Mars. It will include the TWINS instrument (Temperature and Wind sensors for InSight mission) which is an heritage from REMS. The prototype used in the experiments, is composed of three PCBs (Printed Circuit Board) placed on a cylindrical supporting structure (boom) at 120 ¿ from each other. Each PCB contains four Silicon dice set with Platinum resistors that are used as heating elements. The thermal dynamical characterization of one of the dice and its cross-heating with the boom is going to be presented.Postprint (published version

Thermal dynamics modeling of a 3D wind sensor based on hot thin film anemometry

The objective of this paper is to obtain time-varying models of the thermal dynamics of a 3D hot thin film anemometer for Mars atmosphere. To this effect, a proof of concept prototype of the REMS (Rover Environmental Monitoring Station) wind sensor on board the Curiosity rover has been used. The self and cross-heating effects of the thermal structures have been characterized from open-loop measurements using Diffusive Representation. These models have been proven to be suitable in the analysis of the thermal dynamics of the sensor under constant temperature operation employing the tools of Sliding Mode Controllers. This analysis allows to understand the long term heat diffusion processes in the whole structure and how they may affect the raw output signals.Postprint (author's final draft

Sliding mode analysis applied to improve the dynamical response of a spherical 3D wind sensor for Mars atmosphere

The objective of this paper is to show how the structure of a thermal wind anemometer can be tuned to ensure a fast response when the sensor works in closed loop configuration (constant temperature operation). If the thermal filter associated to the sensor structure has only one significative time constant, the resulting system time response, working in closed loop, is enhanced beyond the natural limit imposed by its own thermal circuit. This effect is theoretically explained using the theory of sliding mode controllers. Experimental corroboration is presented by comparing the results obtained with two prototypes of a spherical wind sensor for Mars atmosphere. It will be shown that in case of having only one significant time constant, the time response in closed loop is much faster than the value associated with that time constant. It will be experimentally shown that this effect is lost when the thermal filter has more than one significant time constant. Diffusive representation is used to obtain arbitrary-order models of the thermal structures of the sensors.Preprin

Testing campaign of a martian spherical wind sensor at the AWTSII Wind Tunnel Facility

The purpose of this paper is to present the experimental results obtained with a prototype of a 4-sector spherical anemometer, in the Aarhus Wind Tunnel Simulator II (AWTSII) reproducing Martian conditions. The main objective of the experimental campaign has been to measure wind velocity for a wide number of yaw and pitch angles, in an environment in the range of typical Mars conditions. The experimental results indicate that wind speed and angle recovery can be achieved with the proposed spherical sensor. The obtained responses are close to the empirical models found in the literature.Authors want to show their gratefulness to the Planetary Environment Facilities at Aarhus University (DK) for their hostage and professional approach. This laboratory is a member of Europlanet 2020 RI which has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 654208. This work was partially supported by the Spanish Ministry MINECO under Project grant no. ESP2016-79612-C3-2R.Peer ReviewedPostprint (published version

Heat flow dynamics in thermal systems described by diffusive representation

The objective of this paper is to analyze the dynamics of heat flow in thermal structures working under constant temperature operation. This analysis is made using the tools of sliding mode controllers. The theory is developed considering that the thermal system can be described using diffusive representation. The experimental corroboration has been made with a prototype of a wind sensor for Mars atmosphere being controlled by a thermal sigma-delta modulator. This sensor structure allows to analyze experimentally the time-varying case since changes in wind conditions imply changes in the corresponding thermal models. The diffusive symbols of the experimental structures have been obtained from openloop measurements in which pseudo-random binary sequences of heat are injected in the sensor. With the proposed approach it is possible to predict heat flux transient waveforms in systems described by any arbitrary number of poles. This allows for the first time the analysis of lumped and distributed systems without any limitation on the number of poles describing it.Peer ReviewedPostprint (author's final draft

The effect of curvature in thawing models

We study the evolution of spatial curvature for thawing class of dark energy models. We examine the evolution of the equation of state parameter, $w_\phi$, as a function of the scale factor $a$, for the case in which the scalar field $\phi$ evolve in nearly flat scalar potential. We show that all such models provide the corresponding approximate analytical expressions for $w_\phi(\Omega_\phi,\Omega_k)$ and $w_\phi(a)$. We present observational constraints on these models.Comment: 14 pages, 6 figures. Accepted for publication in Phys. Lett.

Trans-Planckian Physics and the Spectrum of Fluctuations in a Bouncing Universe

In this paper, we calculate the spectrum of scalar field fluctuations in a bouncing, asymptotically flat Universe, and investigate the dependence of the result on changes in the physics on length scales shorter than the Planck length which are introduced via modifications of the dispersion relation. In this model, there are no ambiguities concerning the choice of the initial vacuum state. We study an example in which the final spectrum of fluctuations depends sensitively on the modifications of the dispersion relation without needing to invoke complex frequencies. Changes in the amplitude and in the spectral index are possible, in addition to modulations of the spectrum. This strengthens the conclusions of previous work in which the spectrum of cosmological perturbations in expanding inflationary cosmologies was studied, and it was found that, for dispersion relations for which the evolution is not adiabatic, the spectrum changes from the standard prediction of scale-invariance.Comment: 10 pages, 6 figures, RevTeX4. Analytical determination of the spectrum, corrected some typos, conclusions unchange

The Consistency of Causal Quantum Geometrodynamics and Quantum Field Theory

We consider quantum geometrodynamics and parametrized quantum field theories in the framework of the Bohm-de Broglie interpretation. In the first case, and following the lines of our previous work [1], where a hamiltonian formalism for the bohmian trajectories was constructed, we show the consistency of the theory for any quantum potential, completing the scenarios for canonical quantum cosmology presented there. In the latter case, we prove the consistency of scalar field theory in Minkowski spacetime for any quantum potential, and we show, using this alternative hamiltonian method, a concrete example where Lorentz invariance of individual events is broken.Comment: Final version. See also http://www.cosmologia.cbpf.b

Clusters of Galaxies and the Diffuse Gamma Ray Background

We discuss the diffuse emission of gamma rays and neutrinos from galaxy clusters in the viable models for structure formation in the universe. We use a self-consistent picture for cluster formation and evolution starting from a primordial density perturbation spectrum, and a realistic modelling for the distribution of the intergalactic medium which is abundantly present within galaxy clusters. We find that an evolving population of clusters can produce a fraction $\sim 0.5 \div 2$ of the diffuse gamma-ray background (DGRB) observed by EGRET. This result is robust and is weakly dependent on the cosmological scenario and on the degree of evolution of the inter galactic medium (IGM) in distant clusters, because the bulk of the sources contributing to the DGRB is located at redshifts z \simlt 0.2. We also found a correlation between the non-thermal, gamma-ray and the thermal X-ray emissions from these structures. Using this result, we derived a list of gamma-ray clusters observable with the next generation $\gamma$-ray detectors. Finally, we briefly discuss the possible relevance of galaxy clusters for neutrino astronomy and for very high energy particle astronomy.Comment: 37 pages, 9 Figures, Latex (using elsart,epsfig), to appear in Astroparticle Physics. Send comments to S.Colafrancesco: [email protected]