High-frequency Alfven waves in multi-ion coronal plasma : observational implications

We investigate the effects of high-frequency (of order ion gyrofrequency) Alfvén and ion-cyclotron waves on ion emission lines by studying the dispersion of these waves in a multi-ion coronal plasma. For this purpose we solve the dispersion relation of the linearized multifluid and Vlasov equations in a magnetized multi-ion plasma with coronal abundances of heavy ions. We also calculate the dispersion relation using nonlinear one-dimensional hybrid kinetic simulations of the multi-ion plasma. When heavy ions are present the dispersion relation of parallel propagating Alfvén cyclotron waves exhibits the following branches (in the positive Ω − k quadrant): right-hand polarized nonresonant and left-hand polarized resonant branch for protons and each ion. We calculate the ratio of ion to proton velocities perpendicular to the direction of the magnetic field for each wave modes for typical coronal parameters and find strong enhancement of the heavy ion perpendicular fluid velocity compared with proton perpendicular fluid velocity. The linear multifluid cold plasma results agree with linear warm plasma Vlasov results and with the nonlinear hybrid simulation model results. In view of our findings we discuss how the observed nonthermal line broadening of minor ions in coronal holes may relate to the high-frequency wave motions

The Signs of Life Detector (SOLID): An Instrument to Detect Molecular Biosignatures on Mars

The case for life on Mars grows stronger. Investigations at Gale Crater by Curiosity have revealed fine-grained sedimentary rocks inferred to represent an ancient lake environment suited to support life. In addition, Curiosity tentatively found a heterogeneous distribution of organic carbon within these sediments, consistent with the detection of native organic C in Mars meteorites. Furthermore, modern potentially habitable environments have been recognized on Mars including the N. Polar region visited by Phoenix, gully features suggesting modern water flows, and RSLs that occur seasonally suggest liquid processes. The time is ripe for missions to Mars incorporating a search for biochemical evidence of life

The Icebreaker Mission to Search for Life on Mars

The search for evidence of life on Mars is the ultimate motivation for its scientific exploration. The results from the Phoenix mission indicate that the high N. latitude ice-rich regolith at low elevations is likely to be a recently habitable place on Mars [Stoker et al., 2010]. The near-surface ice likely provided adequate water activity during periods of high obliquity, 3 to 10 Myr ago. Carbon dioxide and nitrogen are present in the atmosphere, and nitrates may be present in the soil. Together with iron in basaltic rocks and perchlorate in the soil they provide carbon and energy sources, and oxidative power to drive metabolism. Furthermore, the presence of organics is possible, as thermally reactive perchlorate would have prevented their detection by Viking and Phoenix. The Mars Icebreaker Life mission [McKay et al., 2013] focuses on the following science goals: (1) Search for biomolecular evidence of life; (2) Search for organic matter from either exogeneous or endogeneous sources using methods that are not effected by the presence of perchlorate; (3) Characterize oxidative species that produced reactivity of soils seen by Viking; and 4) Assess the habitability of the ice bearing soils. The Icebreaker Life payload (Figure 1) includes a 1-m rotary percussive drill that brings cuttings samples to the surface where they are delivered to three instruments (Fig. 1), the Signs of Life Detector (SOLID) [Parro et al., 2011] for biomolecular analysis, Laser Desorption Mass Spectrometer (LDMS) [??? 2015]) for broad spectrum organic analysis, and Wet Chemistry Laboratory (WCL) [Hecht et al., 2009] for detecting soluble species of nutrients and reactive oxidants. The Icebreaker payload fits on the Phoenix spacecraft and can land at the well-characterized Phoe-nix landing site in 2020 in a Discovery-class mission

On the magnetic structure and wind parameter profiles of Alfven wave driven winds in late-type supergiant stars

Cool stars at giant and supergiant evolutionary phases present low velocity and high density winds, responsible for the observed high mass-loss rates. Although presenting high luminosities, radiation pressure on dust particles is not sufficient to explain the wind acceleration process. Among the possible solutions to this still unsolved problem, Alfven waves are, probably, the most interesting for their high efficiency in transfering energy and momentum to the wind. Typically, models of Alfven wave driven winds result in high velocity winds if they are not highly damped. In this work we determine self-consistently the magnetic field geometry and solve the momentum, energy and mass conservation equations, to demonstrate that even a low damped Alfven wave flux is able to reproduce the low velocity wind. We show that the magnetic fluxtubes expand with a super-radial factor S>30 near the stellar surface, larger than that used in previous semi-empirical models. The rapid expansion results in a strong spatial dilution of the wave flux. We obtained the wind parameter profiles for a typical supergiant star of 16 M_sun. The wind is accelerated in a narrow region, coincident with the region of high divergence of the magnetic field lines, up to 100 km/s. For the temperature, we obtained a slight decrease near the surface for low damped waves, because the wave heating mechanism is less effective than the radiative losses. The peak temperature occurs at 1.5 r_0 reaching 6000 K. Propagating outwards, the wind cools down mainly due to adiabatic expansion.Comment: to appear in the MNRA

Structure and Magnetism of well-defined cobalt nanoparticles embedded in a niobium matrix

Our recent studies on Co-clusters embedded in various matrices reveal that the co-deposition technique (simultaneous deposition of two beams : one for the pre-formed clusters and one for the matrix atoms) is a powerful tool to prepare magnetic nanostructures with any couple of materials even though they are miscible. We study, both sharply related, structure and magnetism of the Co/Nb system. Because such a heterogeneous system needs to be described at different scales, we used microscopic and macroscopic techniques but also local selective absorption ones. We conclude that our clusters are 3 nm diameter f.c.c truncated octahedrons with a pure cobalt core and a solid solution between Co and Nb located at the interface which could be responsible for the magnetically inactive monolayers we found. The use of a very diluted Co/Nb film, further lithographed, would allow us to achieve a pattern of microsquid devices in view to study the magnetic dynamics of a single-Co cluster.Comment: 7 TeX pages, 9 Postscript figures, detailed heading adde

Using meteorological measurements from different sources to evaluate the human comfort in urban area

Climate change affects the thermal and human comfort in urban areas. This is more evident in equatorial towns that have experienced, in the last decades, of an increase of air temperature which, acting together with the increasing of the rain rate, generates a strong deterioration of the human comfort. The characterization of the urban heat island is one of the most important points in the agenda of the Research Centers, as well as of the Weather Services of the Nations located in the equatorial area. The Escuela Superior Politecnica del Litoral (Ecuador), jointly with the Instituto Nacional de Meteorologia e Hidrologia (INAMHI - Ecuador) and with the Politecnico di Torino and the Università di Torino (Italy), started a project devoted to the analysis of the thermal comfort in the Guayaquil urban area. The research is funded by the Secretaria de Educacion Superior, Ciencia, Tecnologia e Innovacion (SENESCYT – Ecuador) in the context of the PROMETEO project. The preliminary results of this research show us how, to better describe the thermal comfort in the urban area, it is important to have available the meteorological parameters measured by a meso-network of Automatic Weather Stations. The elaboration of these measures with the Universal Thermal Climate Indices, like the PMV and the PET, provide a detailed analysis of the thermal comfort and of the related human comfort in the urban area. The results of this analysis are to be evaluated jointly with the aerological measurements and with the remote sensing images to characterize correctly the urban heat island

NaI(Tl) Scintillator's Response Functions for Point-like and Distributed Gamma-ray Sources

The response functions of a NaI(Tl) detectors have been estimated using Monte Carlo methods. Response functions were calculated for monoenergetic photon sources (0.05 to 3 MeV). Responses were calculated for point-like sources and for sources distributed in Portland cement cylinders. Calculated responses were used to estimate the detector efficiency for point-like and distributed sources. Samples of cylindrical Portland cement were prepared and exposed to the photoneutron field produced by a 15 MV linac used for radiotherapy. Short half-life radioisotopes were induced and the activity was determined by measuring the pulse-height spectra with a NaI(Tl) g-ray spectrometer that was calibrated using point-like sources. Instead of doing corrections due to differences between the geometry, material and solid angle of point-like sources used for calibration, and the Portland cement cylinders, the detection efficiency was determined using the ratio between the efficiencies for the point-like and the distributed sources estimated with the Monte Carlo calculations, and the activity of the induced isotopes in cement was obtained

Theoretical analysis of flux amplification by soft magnetic material in a putative biological magnetic-field receptor

Birds are endowed with a magnetic sense that allows them to detectEarth’s magnetic field and to use it for orientation. Physiological andbehavioral experiments have shown the upper beak to host amagnetoreceptor. Putative magnetoreceptive structures in the beak arenerve terminals that each contain a dozen or so of micrometer-sizedclusters of superparamagnetic nanocrystals made of magnetite/maghemiteand numerous electron-opaque platelets filled with a so farunidentified, amorphous ferric iron compound. The platelets typicallyform chainlike structures, which have been proposed to function asmagnetic flux focusers for detecting the intensity of the geomagneticfield. Here, we test that proposition from first principles and developan unconstrained model to determine the equilibrium distribution ofmagnetization along a linear chain of platelets which we assume tobehave magnetically soft and to have no magnetic remanence. Ouranalysis, which is valid for arbitrary values of the intrinsic magneticsusceptibility chi, shows that chi needs to be much greater than unityto amplify the external field by two orders of magnitude in a chain ofplatelets. However, the high amplification is confined to the centralregion of the chain and subsides quadratically toward the ends of thechain. For large values of chi, the possibility opens up of realizingmagnetoreceptor mechanisms on the basis of attraction forces betweenadjacent platelets in a linear chain. The force in the central region ofthe chain may amount to several pN, which would be sufficient to convertmagnetic input energy into mechanical output energy. The strikingfeature of an ensemble of platelets is its ability to organize intotightly spaced chains under the action of an external field of givenstrength. We discuss how this property can be exploited for amagnetoreception mechanism

Magnetic Anisotropy of a Single Cobalt Nanoparticle

Using a new microSQUID set-up, we investigate magnetic anisotropy in a single 1000-atoms cobalt cluster. This system opens new fields in the characterization and the understanding of the origin of magnetic anisotropy in such nanoparticles. For this purpose, we report three-dimensional switching field measurements performed on a 3 nm cobalt cluster embedded in a niobium matrix. We are able to separate the different magnetic anisotropy contributions and evidence the dominating role of the cluster surface.Comment: 4 pages, 8 figure