1,821 research outputs found
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 EspĂrito 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 EspĂrito 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 EspĂrito 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
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