30 research outputs found
Dendritic flux penetration in Pb films with a periodic array of antidots
We explore the flux-jump regime in type-II Pb thin films with a periodic
array of antidots by means of magneto-optical measurements. A direct
visualization of the magnetic flux distribution allows to identify a rich
morphology of flux penetration patterns. We determine the phase boundary
between dendritic penetration at low temperatures and a smooth flux
invasion at high temperatures and fields. For the whole range of fields and
temperatures studied, guided vortex motion along the principal axes of the
square pinning array is clearly observed. In particular, the branching process
of the dendrite expansion is fully governed by the underlying pinning topology.
A comparative study between macroscopic techniques and direct local
visualization shed light onto the puzzling and independent magnetic
response observed at low temperatures and fields. Finally, we find that the
distribution of avalanche sizes at low temperatures can be described by a power
law with exponent
The behaviour and productivity of mid-lactation dairy cows provided daily pasture allowance over 2 or 7 intensively grazed strips
Research into the effects of intense grazing regimes on cattle behaviour and productivity will support the ethical intensification of pastoral dairy production. Two treatments were applied to two herds of 30 mid-lactation cows over 28 days. Cows were offered an estimated 12 kg DM/cow (above 5 cm from ground level) of irrigated pasture per day. The control herd received their daily pasture allocation in two equal grazings while the experimental herd received theirs over seven smaller grazings. Backgrazing beyond the current allocation (morning or afternoon) was prevented. Individual records were taken daily for milk production and behaviour (MooMonitor+). Milk composition, energy corrected milk (ECM), and live weight were recorded weekly. Feeding mid-lactation dairy cows over seven smaller grazing allocations reduced the time cows spent ruminating (p p p p > 0.05). Cattle may have adapted their ingestive behaviour in response to the more intensive strip-grazing regime utilised in this study, with negative consequences for digestive processes and consequently milk production. Intense grazing regimes need to support the ingestive, digestive, and social behaviours of cattle
Guided vortex motion in superconductors with a square antidot lattice
We have measured the in-plane anisotropy of the vortex mobility in a thin Pb
film with a square array of antidots. The Lorentz force, acting on the
vortices, was rotated by adding two perpendicular currents and keeping the
amplitude of the net current constant. One set of voltage probes was used to
detect the vortex motion. We show that the pinning landscape provided by the
square antidot lattice influences the vortex motion in two different ways.
First, the modulus of the vortex velocity becomes angular dependent with a
lower mobility along the diagonals of the pinning array. Second, the vortex
displacement is preferentially parallel to the principal axes of the underlying
pinning lattice, giving rise to a misalignment between the vortex velocity and
the applied Lorentz force. We show that this anisotropic vortex motion is
temperature dependent and progressively fades out when approaching the normal
state.Comment: 5 pages, 4 figure
Genetic diversity in reintroduced and restocked polpulations of the common hamster (cricetus cricetus
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In-plane anisotropic vortex motion induced by a square array of antidots
We report on electro-transport measurements on a Pb thin film with a square array of antidots, for the whole angular range of in-plane current orientations. We demonstrate that the interaction of a moving flux line lattice with a periodic pinning potential, breaks the rotational symmetry and induces a guided vortex motion along the principal symmetry orientations of the pinning array. As a consequence, we found that for orientations different than the symmetry directions, the vortex velocity is not aligned with the Lorentz force. We show that this anisotropic vortex motion is temperature dependent and progressively fades out when approaching the normal state. (C) 2004 Elsevier B.V. All rights reserved
Flux pinning properties of holes and blind holes arranged periodically in a superconductor
We investigate the dynamic response of a vortex lattice in nanostructured superconducting Pb films by means of ac-magnetization measurements. We compare the flux pinning properties of superconducting Pb films with arrays of fully perforated holes (antidots) and partially drilled holes (blind holes). Our results show that an array of blind holes, characterized by a thin superconducting bottom layer, gives rise to a less efficient pinning potential than an array of antidots. On top of that, a lower number of flux quanta trapped per pinning site (the saturation number), is observed for the blind hole array. (C) 2004 Elsevier B.V. All rights reserved