2,218 research outputs found
Modelling survival and connectivity of Mnemiopsis leidyi in the south-western North Sea and Scheldt estuaries
Three different models were applied to study the reproduction, survival and dispersal of Mnemiopsis leidyi in the Scheldt estuaries and the southern North Sea: a high-resolution particle tracking model with passive particles, a low-resolution particle tracking model with a reproduction model coupled to a biogeochemical model, and a dynamic energy budget (DEB) model. The results of the models, each with its strengths and weaknesses, suggest the following conceptual situation: (i) the estuaries possess enough retention capability to keep an overwintering population, and enough exchange with coastal waters of the North Sea to seed offshore populations; (ii) M. leidyi can survive in the North Sea, and be transported over considerable distances, thus facilitating connectivity between coastal embayments; (iii) under current climatic conditions, M. leidyi may not be able to reproduce in large numbers in coastal and offshore waters of the North Sea, but this may change with global warming; however, this result is subject to substantial uncertainty. Further quantitative observational work is needed on the effects of temperature, salinity and food availability on reproduction and on mortality at different life stages to improve models such as used here
In-plane field-induced vortex liquid correlations in underdoped Bi_2Sr_2CaCu_2O_8+\delta
The effect of a magnetic field component parallel to the superconducting
layers on longitudinal Josephson plasma oscillations in the layered high
temperature superconductor BiSrCaCuO is shown to
depend on the thermodynamic state of the underlying vortex lattice. Whereas the
parallel magnetic field component depresses the Josephson Plasma Resonance
(JPR) frequency in the vortex solid phase, it may enhance it in the vortex
liquid. There is a close correlation between the behavior of microwave
absorption near the JPR frequency and the effectiveness of pancake vortex
pinning, with the enhancement of the plasma resonance frequency occurring in
the absence of pinning, at high temperature close to the vortex melting line.
An interpretation is proposed in terms of the attraction between pancake
vortices and Josephson vortices, apparently also present in the vortex liquid
state.Comment: 8 pages, 7 Figures, submitted to Phys. Rev.
Thermodynamics of the vortex liquid in heavy ion-irradiated superconductors
It is shown that the large effect of heavy ion-irradiation on the
thermodynamical properties of the anisotropic superconductor
YBaCuO extends well into the superconducting
fluctuation regime. The presence of the induced amorphous columnar defects
shifts the specific heat maximum at the normal-to-superconducting transition.
This effect is similar to that recently put into evidence in cubic
KBaBiO (). In both compounds, vortex pinning
manifests itself as a sharp angular dependence of the \em equilibrium \rm
torque. In YBaCuO, pinning by the defects appears at
the temperature of the specific heat maximum, well above the
magnetic irreversibility line . In isotropic
KBaBiO, the onset of the pinning-related torque anomaly
tracks the onset of the specific heat anomaly and the irreversibility line. In
YBaCuO, fluctuations of the amplitude of the order
parameter (and not vortex line wandering) are ultimately responsible for the
vanishing of pinning. In KBaBiO, vortex pinning disappears
only at the superconducting-to-normal transition. The results indicate that in
both compounds, the pinning energy at the ``Bose glass'' transition is large
with respect to the total free energy gain in the superconducting state. By
implication, the mechanism of this latter transition should be reconsidered.Comment: 9 pages, 9 figures, resubmitted to PRB 23-09-200
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