Experimental Evidence of Critical Sensitivity in Catastrophe

The paper presents an experimental study on critical sensitivity in rocks. Critical sensitivity means that the response of a system to external controlling variable may become significantly sensitive as the system approaches its catastrophic rupture point. It is found that the sensitivities measured by responses on three scales (sample scale, locally macroscopic scales and mesoscopic scale) display increase prior to catastrophic transition point. These experimental results do support the concept that critical sensitivity might be a common precursory feature of catastrophe. Furthermore, our previous theoretical model is extended to explore the fluctuations in critical sensitivity in the rock tests.

Juvenile and small resident fishes of Florida Bay, a critical habitat in the Everglades National Park, Florida

This compendium presents information on the life history, diet, and abundance and distribution of 46 of the more abundant juvenile and small resident fish species, and data on three species of seagrasses in Florida Bay, Everglades National Park. Abundance and distribution of fish data were derived from three sampling schemes: (1) an otter trawl in basins (1984–1985, 1994–2001), (2) a surface trawl in basins (1984–1985), and (3) a surface trawl in channels (1984–1985). Results from surface trawling only included pelagic species. Collections made with an otter trawl in basins on a bi-monthly basis were emphasized. Nonparametric statistics were used to test spatial and temporal differences in the abundance of species and seagrasses. Fish species accounts were presented in four sections – Life history, Diet, Abundance and distribution, and Length-frequency distributions. Although Florida Bay is a subtropical estuary, the majority of fish species (76%) had warm-temperate affinities; i.e., only 24% were solely tropical species. The five most abundant species collected, in descending order, by (1) otter trawl in basins were: Eucinostomus gula, Lucania parva, Anchoa mitchilli, Lagodon rhomboides, and Syngnathus scovelli; (2) surface trawl in basins were: Hyporhamphus unifasciatus, Strongylura notata, Chriodorus atherinoides, Anchoa hepsetus, and Atherinomorus stipes; (3) surface trawl in channels were: Hypoatherina harringtonensis, A. stipes, A. mitchelli, H. unifasciatus, and C. atherinoides. (PDF file contains 219 pages.)

Critical current anisotropy in high temperature superconductors

After nearly 15 years of research effort, High Temperature Superconductors (HTS) are finding a wide range of practical applications. A clear understanding of the factors controlling the current carrying capacity of these materials is a prerequisite to their successful technological development. The critical current density (Jc) in HTS is directly dependent on the structure and pinning of the Flux Line Lattice (FLL) in these materials. This thesis presents an investigation of the Jc anisotropy in HTS. The use of thin films grown on off c-axis (vicinal) substrates allowed the effect of current directions outside the cuprate planes to be studied. With this experimental geometry Berghuis, et al. (Phys. Rev. Lett. 79, 12, pg. 2332) observed a striking flux channelling effect in vicinal YBa2Cu3O7-δ (YBCO) films. By confirming, and extending, this observation, it is demonstrated that this is an intrinsic effect. The results obtained, appear to fit well with the predictions of a field angle dependent cross-over from a three dimensional rectilinear FLL to a kinked lattice of strings and pancakes. The pinning force density for movement of strings inside the cuprate planes is considerably less than that on vortex pancake elements. When the FLL is entirely string-like this reduced pinning leads to the observed channelling minima. It is observed that anti-phase boundaries enhance the Jc in vicinal YBCO films by strongly pinning vortex strings. The effect on the FLL structure cross-over of increasing anisotropy has been elucidated using de-oxygenated vicinal YBCO films. Intriguingly, the counter intuitive prediction that the range of applied field angle for which the kinked lattice is fully developed reduces with increasing anisotropy, appears to be confirmed. Although vortex channelling cannot be observed in c-axis YBCO films, the pinning force density for vortex string channelling has been extracted by observing string dragging. By studying the effect of rotating the applied field at a constant angle to the cuprate planes, it is possible to observe the cross-over into the string pancake regime in c-axis films. In the 3D region, the observed behaviour is well explained by the anisotropic Ginzburg-Landau model. Measurements were also made on thin films of the much more anisotropic Bi 2Sr2CaCu2O8+x material, grown on vicinal substrates. The absence of any flux channelling effect and clear adherence to the expected Kes-Law behaviour in the observed Jc characteristics does not provide evidence for the existence of the predicted ‘crossing lattice’ in Bi 2Sr2CaCu2O8+x .

The precautionary approach and the management of the European eel (Anguilla anguilla) – critical remarks

Recruitment and commercial catches of European eel have been in decline since the late 1970s. So far, the reasons are not well understood. A range of potential natural and anthropogenic reasons have been discussed, but the relative importance of the factors is unknown. As a consequence of the decline in recruitment an urgent need for protective management measures was concluded. The main approach is to restrict the fishery on eel, in particular with reference to the precautionary approach. However, in view of the lack of knowledge on the factors responsible for the recruitment decline and by considering that many yellow and silver eel stocks in freshwaters depend on restocking by the fishery, such simplified conclusions are critically discussed. A concept for the sustainable management of eel has to include 1) research on the factors determining the population dynamics, in particular during the oceanic stages, 2) a stronger consideration of socio-economic aspects, and 3) intensified research on artificial reproduction and rearing of eel.

Numerical Study on Critical Wedge Angle of Cellular Detonation Reflections

The critical wedge angle (CWA) for the transition from regular reflection (RR) to Mach reflection (MR) of a cellular detonation wave is studied numerically by an improved space-time conservation element and solution element method together with a two-step chemical reaction model. The accuracy of that numerical way is verified by simulating cellular detonation reflections at a 19.3∘ wedge. The planar and cellular detonation reflections over 45∘–55∘ wedges are also simulated. When the cellular detonation wave is over a 50∘ wedge, numerical results show a new phenomenon that RR and MR occur alternately. The transition process between RR and MR is investigated with the local pressure contours. Numerical analysis shows that the cellular structure is the essential reason for the new phenomenon and the CWA of detonation reflection is not a certain angle but an angle range.

Investigation on mechanism of critical cavitating flow in liquid jet pumps under operating limits

The critical cavitating flow in liquid jet pumps under operating limits is investigated in this paper. Measurements on the axial pressure distribution along the wall of jet pumps indicate that two-phase critical flow occurs in the throat pipe under operating limits. The entrained flow rate and the distribution of the wall pressure upstream lowest pressure section does not change when the outlet pressure is lower than a critical value. A liquid-vapor mixing shockwave is also observed under operating limits. The wave front moves back and forth in low frequency around the position of the lowest pressure. With the measured axial wall pressures, the Mach number of the two-phase cavitating flow is calculated. It's found that the maximum Mach number is very close to I under operating limits. Further analysis infers a cross-section where Mach number approaches to I near the wave front. Thus, the liquid-vapor mixture velocity should reach the local sound velocity and resulting in the occurrence of operating limits.