Vortex Lattice Melting of a NbSe2 single grain probed by Ultrasensitive Cantilever Magnetometry

Using dynamic cantilever magnetometry, we study the vortex lattice and its corresponding melting transition in a micrometer-size crystallite of superconducting NbSe2. Measurements of the cantilever resonance frequency as a function of magnetic field and temperature respond to the magnetization of the vortex-lattice. The cantilever dissipation depends on thermally activated vortex creep motion, whose pinning energy barrier is found to be in good agreement with transport measurements on bulk samples. This approach reveals the phase diagram of the crystallite, and is applicable to other micro- or nanometer-scale superconducting samples.Comment: 5 pages, 4 figure

Ecology and conservation of the leatherback sea turtle (Dermochelys coriacea) nesting in Brazil

Knowledge of life-history parameters of marine turtles is essential for understanding their ecology and for effective conservation. The leatherback turtle (Dermochelys coriacea) is globally classified as Vulnerable by the International Union of Conservation of Nature (IUCN), however, distinct subpopulations are recognised and require specific data for the assessment of their conservation status. The Southwest Atlantic Ocean subpopulation is known to regularly nest only in eastern Brazil, on the coast of the state of Espírito Santo. This thesis presents a collection of chapters that investigate the ecology and conservation of this taxon. Multiple technologies and methodologies are employed to ask both ecological and management questions, assessing key population parameters to inform conservation. Here I use long-term data (30 years) to investigate the nesting ecology, population trends and conservation status of leatherback turtles in Espírito Santo. I explore their nesting environment and provide baseline data which will guide further research and management strategies under future scenarios of climate change. I investigate the marine habitat use through stable isotope approaches and satellite telemetry to infer spatial ecology, setting out the conservation situation and perspectives of this important population. Finally, I assess the potential impacts of artificial light on wildlife, using marine turtles in Brazil as a case study. The leatherback turtle rookery in Espírito Santo shows signs of population recovery, however, the existence of various threats means this population remains subject of conservation concern.Conselho Nacional de Desenvolvimento Cientifico eTecnologic

Genome size in Calomys laucha and Calomys musculinus (Rodentia, Cricetidae)

International audienc

Feedback cooling of a cantilever's fundamental mode below 5 mK

We cool the fundamental mechanical mode of an ultrasoft silicon cantilever from a base temperature of 2.2 K to 2.9 +/- 0.3 mK using active optomechanical feedback. The lowest observed mode temperature is consistent with limits determined by the properties of the cantilever and by the measurement noise. For high feedback gain, the driven cantilever motion is found to suppress or "squash" the optical interferometer intensity noise below the shot noise level.Comment: 4 pages, 6 figure

Nuclear spin relaxation induced by a mechanical resonator

We report on measurements of the spin lifetime of nuclear spins strongly coupled to a micromechanical cantilever as used in magnetic resonance force microscopy. We find that the rotating-frame correlation time of the statistical nuclear polarization is set by the magneto-mechanical noise originating from the thermal motion of the cantilever. Evidence is based on the effect of three parameters: (1) the magnetic field gradient (the coupling strength), (2) the Rabi frequency of the spins (the transition energy), and (3) the temperature of the low-frequency mechanical modes. Experimental results are compared to relaxation rates calculated from the spectral density of the magneto-mechanical noise.Comment: 4 pages, 4 figure

Force-detected nuclear double resonance between statistical spin polarizations

We demonstrate nuclear double resonance for nanometer-scale volumes of spins where random fluctuations rather than Boltzmann polarization dominate. When the Hartmann-Hahn condition is met in a cross-polarization experiment, flip-flops occur between two species of spins and their fluctuations become coupled. We use magnetic resonance force microscopy to measure this effect between 1H and 13C spins in 13C-enriched stearic acid. The development of a cross-polarization technique for statistical ensembles adds an important tool for generating chemical contrast in nanometer-scale magnetic resonance.Comment: 14 pages, 4 figure