Mitigating the negative impacts of tall wind turbines on bats: Vertical activity profiles and relationships to wind speed.

Wind turbines represent a source of hazard for bats, especially through collision with rotor blades. With increasing technical development, tall turbines (rotor-swept zone 50-150 m above ground level) are becoming widespread, yet we lack quantitative information about species active at these heights, which impedes proposing targeted mitigation recommendations for bat-friendly turbine operation. We investigated vertical activity profiles of a bat assemblage, and their relationships to wind speed, within a major valley of the European Alps where tall wind turbines are being deployed. To monitor bat activity we installed automatic recorders at sequentially increasing heights from ground level up to 65 m, with the goal to determine species-specific vertical activity profiles and to link them to wind speed. Bat call sequences were analysed with an automatic algorithm, paying particular attention to mouse-eared bats (Myotis myotis and Myotis blythii) and the European free-tailed bat (Tadarida teniotis), three locally rare species. The most often recorded bats were the Common pipistrelle (Pipistrellus pipistrellus) and Savi's pipistrelle (Hypsugo savii). Mouse-eared bats were rarely recorded, and mostly just above ground, appearing out of risk of collision. T. teniotis had a more evenly distributed vertical activity profile, often being active at rotor level, but its activity at that height ceased above 5 ms-1 wind speed. Overall bat activity in the rotor-swept zone declined with increasing wind speed, dropping below 5% above 5.4 ms-1. Collision risk could be drastically reduced if nocturnal operation of tall wind turbines would be restricted to wind speeds above 5 ms-1. Such measure should be implemented year-round because T. teniotis remains active in winter. This operational restriction is likely to cause only small energy production losses at these tall wind turbines, although further analyses are needed to assess these losses precisely

Non-resonant microwave absorption studies of superconducting MgB_2

Non-resonant microwave absorption(NRMA) studies of superconducting MgB_2 at a frequency of 9.43 GHz in the field range -50 Gauss to 5000 Gauss are reported. The NRMA results indicate near absence of intergranular weak links. A linear temperature dependence of the lower critical field H_c1 is observed indicating a non s-wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d-wave symmetry is also not observed.Comment: 8 pages, 2 figure

Detailed investigation of the superconducting transition of niobium disks exhibiting the paramagnetic Meissner effect

The superconducting transition region in a Nb disk showing the paramagnetic Meissner effect (PME) has been investigated in detail. From the field-cooled magnetization behavior, two well-defined temperatures can be associated with the appearance of the PME: T_1 (< T_c) indicates the characteristic temperature where the paramagnetic moment first appears and a lower temperature T_p (< T_1) defines the temperature where the positive moment no longer increases. During the subsequent warming, the paramagnetic moment begins to decrease at T_p and then vanishes at T_1 with the magnitude of the magnetization change between these two temperatures being nearly the same as that during cooling. This indicates that the nature of the PME is reversible and not associated with flux motion. Furthermore, the appearance of this paramagnetic moment is even observable in fields as large as 0.2 T even though the magnetization does not remain positive to the lowest temperatures. Magnetic hysteresis loops in the temperature range between T_1 and T_p also exhibit a distinct shape that is different from the archetypal shape of a bulk type-II superconductor. These behaviors are discussed in terms of the so-called 'giant vortex state'.Comment: Total 4 printed pages, 4 Figure

Strong rejuvenation in a chiral-glass superconductor

The glassy paramagnetic Meissner phase of a Bi$_2$Sr$_2$CaCu$_2$O$_x$ superconductor ($x$ = 8.18) is investigated by squid magnetometry, using ``dc-memory'' experiments employed earlier to study spin glasses. The temperature dependence of the zero-field-cooled and thermo-remanent magnetization is recorded on re-heating after specific cooling protocols, in which single or multiple halts are performed at constant temperatures. The 'spin' states equilibrated during the halts are retrieved on re-heating. The observed memory and rejuvenation effects are similar to those observed in Heisenberg-like spin glasses.Comment: REVTeX 4 style; 5 pages, 5 figure

Paramagnetic Meissner Effect in Multiply-Connected Superconductors

We have measured a paramagnetic Meissner effect in Nb-Al2O3-Nb Josephson junction arrays using a scanning SQUID microscope. The arrays exhibit diamagnetism for some cooling fields and paramagnetism for other cooling fields. The measured mean magnetization is always less than 0.3 flux quantum (in terms of flux per unit cell of the array) for the range of cooling fields investigated. We demonstrate that a new model of magnetic screening, valid for multiply-connected superconductors, reproduces all of the essential features of paramagnetism that we observe and that no exotic mechanism, such as d-wave superconductivity, is needed for paramagnetism.Comment: 4 pages, 3 figures, LaTe

Induced paramagnetic states by localized π\pi -loops in grain boundaries

Recent experiments on high-temperature superconductors show paramagnetic behavior localized at grain boundaries (GB). This paramagnetism can be attributed to the presence unconventional d-wave induced $\pi$-junctions. By modeling the GB as an array of $\pi$ and conventional Josephson junction we determine the conditions of the occurrence of the paramagnetic behavior.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let

Vortices and Quantum tunneling in Current-Biased 0-\pi-0 Josephson Junctions of d-wave Superconductors

We study a current-biased 0-\pi-0 Josephson junction made by high-T_c superconductors, theoretically. When a length of the \pi junction is large enough, this junction contains a vortex-antivortex pair at both ends of the \pi junction. Magnetic flux carried by the vortices is calculated using the sine-Gordon equation. The result shows that the magnetic flux of the vortices is suppressed to zero as the distance between the vortices is reduced. By applying an external current, the orientation of the vortices is reversed, and a voltage pulse is generated. The current needed for this transition and generated pulse energy are calculated. Macroscopic quantum tunneling (MQT) in this transition is also studied. The tunneling rate has been evaluated by an effective Hamiltonian with one degree of freedom.Comment: 12 pages, LaTeX with 5 PS figures, using jpsj.st

Aging Effect in Ceramic Superconductors

A three-dimensional lattice of the Josephson junctions with a finite self-conductance is employed to model ceramic superconductors. Using Monte Carlo simulations it is shown that the aging disappears in the strong screening limit. In the weeak screening regime aging is present even at low temperatures. For intermediate values of the self-inductance aging occurs at intermediate temperatures interval but is suppressed entirely at high and low temperatures. Our results are in good agreement with experiments.Comment: 5 pages, 5 eps figures, to appear in Physical Review Letter

Phenomenological theory of the 3 Kelvin phase in Sr2RuO4

We model the 3K-phase of Sr2RuO4 with Ru-metal inclusion as interface state with locally enhanced transition temperatures. The resulting 3K-phase must have a different pairing symmetry than the bulk phase of Sr2RuO4, because the symmetry at the interface is lower than in the bulk. It is invariant under time reversal and a second transition, in general, above the onset of bulk superconductivity is expected where time reversal symmetry is broken. The nucleation of the 3K-phase exhibits a ``capillary effect'' which can lead to frustration phenomena for the superconducting states on different Ru-inclusions. Furthermore, the phase structure of the pair wave function gives rise to zero-energy quasiparticle states which would be visible in quasiparticle tunneling spectra. Additional characteristic properties are associated with the upper critical field Hc2. The 3K-phase has a weaker anisotropy of Hc2 between the inplane and z-axis orientation than the bulk superconducting phase. This is connected with the more isotropic nature Ru-metal which yields a stronger orbital depairing effect for the inplane magnetic field than in the strongly layered Sr$_2RuO4. An anomalous temperature dependence for the z-axis critical field is found due to the coupling of the magnetic field to the order parameter texture at the interface. Various other experiments are discussed and new measurements are suggested.Comment: 10 pages, 5 figure

Reentrant AC magnetic susceptibility in Josephson-junction arrays: An alternative explanation for the paramagnetic Meissner effect

The paramagnetic Meissner effect (PME) measured in high $T_{C}$ granular superconductors has been attributed to the presence of $\pi$-junctions between the grains. Here we present measurements of complex AC magnetic susceptibility from two-dimensional arrays of conventional (non $\pi$) Nb/Al/AlOx/Nb Josephson junctions. We measured the susceptibility as a function of the temperature $T$, the AC amplitude of the excitation field, $h_{AC}$, and the external magnetic field, $H_{DC}$. The experiments show a strong paramagnetic contribution from the multi-junction loops, which manifests itself as a reentrant screening at low temperature, for values of $h_{AC}$ higher than 50 mOe. A highly simplified model, based on a single loop containing four junction, accounts for this paramagnetic contribution and the range of parameters in which it appears. This model offers an alternative explanation of PME which does not involve $\pi$-junctions.Comment: PDF file, 6 two-columns pages, 9 figure