2,496 research outputs found
Nanoengineered magnetic-field-induced superconductivity
The perpendicular critical fields of a superconducting film have been
strongly enhanced by using a nanoengineered lattice of magnetic dots (dipoles)
on top of the film. Magnetic-field-induced superconductivity is observed in
these hybrid superconductor / ferromagnet systems due to the compensation of
the applied field between the dots by the stray field of the dipole array. By
switching between different magnetic states of the nanoengineered field
compensator, the critical parameters of the superconductor can be effectively
controlled.Comment: 4 pages, 4 figure
Muscle Non-shivering Thermogenesis and Its Role in the Evolution of Endothermy
The development of sustained, long-term endothermy was one of the major transitions in the evolution of vertebrates. Thermogenesis in endotherms does not only occur via shivering or activity, but also via non-shivering thermogenesis (NST). Mammalian NST is mediated by the uncoupling protein 1 in the brown adipose tissue (BAT) and possibly involves an additional mechanism of NST in skeletal muscle. This alternative mechanism is based on Ca2+-slippage by a sarcoplasmatic reticulum Ca2+-ATPase (SERCA) and is controlled by the protein sarcolipin. The existence of muscle based NST has been discussed for a long time and is likely present in all mammals. However, its importance for thermoregulation was demonstrated only recently in mice. Interestingly, birds, which have evolved from a different reptilian lineage than mammals and lack UCP1-mediated NST, also exhibit muscle based NST under the involvement of SERCA, though likely without the participation of sarcolipin. In this review we summarize the current knowledge on muscle NST and discuss the efficiency of muscle NST and BAT in the context of the hypothesis that muscle NST could have been the earliest mechanism of heat generation during cold exposure in vertebrates that ultimately enabled the evolution of endothermy. We suggest that the evolution of BAT in addition to muscle NST was related to heterothermy being predominant among early endothermic mammals. Furthermore, we argue that, in contrast to small mammals, muscle NST is sufficient to maintain high body temperature in birds, which have enhanced capacities to fuel muscle NST by high rates of fatty acid import
Scaling of spontaneous rotation with temperature and plasma current in tokamaks
Using theoretical arguments, a simple scaling law for the size of the
intrinsic rotation observed in tokamaks in the absence of momentum injection is
found: the velocity generated in the core of a tokamak must be proportional to
the ion temperature difference in the core divided by the plasma current,
independent of the size of the device. The constant of proportionality is of
the order of . When the
intrinsic rotation profile is hollow, i.e. it is counter-current in the core of
the tokamak and co-current in the edge, the scaling law presented in this
Letter fits the data remarkably well for several tokamaks of vastly different
size and heated by different mechanisms.Comment: 5 pages, 3 figure
Geosynthetic landfill cap stability: comparison of limit equilibrium, computational limit analysis and finite-element analyses
The stability of the veneer cover soil (landfill cap) is an important issue in landfill design. Incorrect design of the landfill cap can lead to failure, which may result in the veneer cover soil sliding on an underlying geosynthetic layer, or in tension failure of the geosynthetic itself. Previous limit equilibrium (LE) analyses of veneer cover layer stability presented in the literature have generally considered whole-slope failure. In this paper, modified LE equations are proposed that (a) encompass more critical cases of localised slope failure for specific cases, and (b) are calibrated against two other methods: 2-D computational limit analysis (CLA) using LimitState:GEO and 2-D elasto-plastic finite-element (FE) analysis using PLAXIS. The scenarios examined encompass a cover of uniform thickness, a buttressed cover, a cover of tapered thickness, the effects of seepage forces, and the effects of construction equipment. It is shown that the LE method provides a reasonable estimate of veneer cover layer stability for most cases examined, although it is in general non-conservative, relative to the CLA and FE analyses. Local failure was found to be critical in the case of the construction equipment, buttress and horizontal seepage scenarios. In the latter case the LE equations previously presented in the literature significantly overestimate stability compared with the LE, CLA and FE analyses considered in this paper
Superconducting crossed correlations in ferromagnets: implications for thermodynamics and quantum transport
It is demonstrated that non local Cooper pairs can propagate in ferromagnetic
electrodes having an opposite spin orientation. In the presence of such crossed
correlations, the superconducting gap is found to depend explicitly on the
relative orientation of the ferromagnetic electrodes. Non local Cooper pairs
can in principle be probed with dc-transport. With two ferromagnetic
electrodes, we propose a ``quantum switch'' that can be used to detect
correlated pairs of electrons. With three or more ferromagnetic electrodes, the
Cooper pair-like state is a linear superposition of Cooper pairs which could be
detected in dc-transport. The effect also induces an enhancement of the
ferromagnetic proximity effect on the basis of crossed superconducting
correlations propagating along domain walls.Comment: 4 pages, RevTe
Mesoscopic Ferromagnet/Superconductor Junctions and the Proximity Effect
We have measured the electrical transport of submicron ferromagnets (Ni) in
contact with a mesoscopic superconductor (Al) for a range of interface
resistances. In the geometry measured, the interface and the ferromagnet are
measured separately. The ferromagnet itself shows no appreciable
superconducting proximity effect, but the ferromagnet/superconductor interface
exhibits strong temperature, field and current bias dependences. These effects
are dependent on the local magnetic field distribution near the interface
arising from the ferromagnet. We find that the temperature dependences may be
fit to a modified version of the Blonder-Tinkham-Klapwijk theory for
normal-superconductor transport.Comment: 4 eps fig
Sub-gap conductance in ferromagnetic-superconducting mesoscopic structures
We study the sub-gap conductance of a ferromagnetic mesoscopic region
attached to a ferromagnetic and a superconducting electrode by means of tunnel
junctions. In the absence of the exchange field, the ratio of the two tunnel junction resistances determines the behaviour of
the sub-gap conductance which possesses a zero-bias peak for and for
a peak at finite voltage. We show that the inclusion of the exchange
field leads to a peak splitting for , while it shifts the zero-bias
anomaly to finite voltages for .Comment: 5 pages revte
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