4,333 research outputs found
Domain wall displacement in Py square ring for single nanometric magnetic bead detection
A new approach based on the domain wall displacement in confined
ferromagnetic nanostructures for attracting and sensing a single nanometric
magnetic particles is presented. We modeled and experimentally demonstrated the
viability of the approach using an anisotropic magnetoresistance device made by
a micron-size square ring of Permalloy designed for application in magnetic
storage. This detection concept can be suitable to biomolecular recognition,
and in particular to single molecule detection.Comment: 8pages, 3figure
Stably accessing octave-spanning microresonator frequency combs in the soliton regime
Microresonator frequency combs can be an enabling technology for optical
frequency synthesis and timekeeping in low size, weight, and power
architectures. Such systems require comb operation in low-noise, phase-coherent
states such as solitons, with broad spectral bandwidths (e.g., octave-spanning)
for self-referencing to detect the carrier-envelope offset frequency. However,
stably accessing such states is complicated by thermo-optic dispersion. For
example, in the Si3N4 platform, precisely dispersion-engineered structures can
support broadband operation, but microsecond thermal time constants have
necessitated fast pump power or frequency control to stabilize the solitons. In
contrast, here we consider how broadband soliton states can be accessed with
simple pump laser frequency tuning, at a rate much slower than the thermal
dynamics. We demonstrate octave-spanning soliton frequency combs in Si3N4
microresonators, including the generation of a multi-soliton state with a pump
power near 40 mW and a single-soliton state with a pump power near 120 mW. We
also develop a simplified two-step analysis to explain how these states are
accessed in a thermally stable way without fast control of the pump laser, and
outline the required thermal properties for such operation. Our model agrees
with experimental results as well as numerical simulations based on a
Lugiato-Lefever equation that incorporates thermo-optic dispersion. Moreover,
it also explains an experimental observation that a member of an adjacent mode
family on the red-detuned side of the pump mode can mitigate the thermal
requirements for accessing soliton states
Dipole-induced vortex ratchets in superconducting films with arrays of micromagnets
We investigate the transport properties of superconducting films with
periodic arrays of in-plane magnetized micromagnets. Two different magnetic
textures are studied: a square array of magnetic bars and a close-packed array
of triangular microrings. As confirmed by MFM imaging, the magnetic state of
both systems can be adjusted to produce arrays of almost point-like magnetic
dipoles. By carrying out transport measurements with ac drive, we observed
experimentally a recently predicted ratchet effect induced by the interaction
between superconducting vortices and the magnetic dipoles. Moreover, we find
that these magnetic textures produce vortex-antivortex patterns, which have a
crucial role on the transport properties of this hybrid system.Comment: 4 pages, 4 figure
Geometry of lines and degeneracy loci of morphisms of vector bundles
Corrado Segre played a leading role in the foundation of line geometry. We
survey some recent results on degeneracy loci of morphisms of vector bundles
where he still is of profound inspiration.Comment: 10 pages. To appear in the proceedings of the conference "Homage to
Corrado Segre
A randomised controlled trial of a blended learning education intervention for teaching evidence-based medicine
Subnanometer traceability of localization microscopy
In localization microscopy, subnanometer precision is possible but supporting
accuracy is challenging, and no study has demonstrated reliable traceability to
the International System of Units (SI). To do so, we measure the positions of
nanoscale apertures in a reference array by traceable atomic-force microscopy,
creating a master standard. We perform correlative measurements of this
standard by optical microscopy, correcting position errors from optical
aberrations by a Zernike calibration. We establish an uncertainty field due to
localization errors and scale uncertainty, with regions of position
traceability to within a 68 % coverage interval of +/- 1.0 nm. These results
enable localization metrology with high throughput, which we apply to measure
working standards, validating the subnanometer accuracy of lithographic pitch
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