Landau, Abrikosov, Hofstadter: Magnetic Flux Penetration in a Lattice Superconductor

Magnetic flux penetration in superconductors involves a rich variety of subtle phenomena, much of which is still poorly understood. Here these complexities are studied by formulating the Ginzburg-Landau equations as a lattice gauge theory. Their solutions are compared and contrasted with the (heuristic) Landau model of type I superconductivity, and the (perturbative) Abrikosov model for type II superconductors. Novelties arise as the continuum limit is approached, related to an effect discovered by Hofstadter. Various cautionary remarks pertinent to large-scale simulations are made

A Comparison of Video and Accelerometer Based Approaches Applied to Performance Monitoring in Swimming.

The aim of this paper is to present a comparison of video- and sensor based studies of swimming performance. The video-based approach is reviewed and contrasted to the newer sensor-based technology, specifically accelerometers based upon Micro-Electro-Mechanical Systems (MEMS) technology. Results from previously published swim performance studies using both the video and sensor technologies are summarised and evaluated against the conventional theory that upper arm movements are of primary interest when quantifying free-style technique. The authors conclude that multiple sensor-based measurements of swimmers’ acceleration profiles have the potential to offer significant advances in coaching technique over the traditional video based approach

Phase Diagrams of Bi1-xSbx Thin Films with Different Growth Orientations

A closed-form model is developed to evaluate the band-edge shift caused by quantum confinement for a two-dimensional non-parabolic carrier-pocket. Based on this model, the symmetries and the band-shifts of different carrier-pockets are evaluated for BiSb thin films that are grown along different crystalline axes. The phase diagrams for the BiSb thin film systems with different growth orientations are calculated and analyzed

Variation in Leaf Structure and Function in Quercus Douglasii Trees Differing in Root Architecture and Drought History

Seasonal changes in leaf specific mass, nitrogen, chlorophyll, and photosynthetic properties were measured for two groups of spatially intermixed Quercus douglasii trees with different drought histories and apparently different root architectures. One group, referred to as \u27\u27high-psi(pd) trees, included trees with low amounts of fine root biomass in the upper 50 cm of soil and high predawn xylem pressure potentials (psi(pd)) during summer drought. These two characteristics indicate that trees in this group have deep roots, which may reach the water table. The second group, referred to as \u27\u27low-psi(pd) trees, had three to five times higher fine root biomass in the upper 50 cm of soil and low psi(pd) during summer drought. These two characteristics indicate that these trees may not have access to the water table and are dependent on shallow soil moisture, which decreases rapidly during the rainless summers of central California. In the spring, after the full expansion of new leaves, but prior to significant divergence in psi(pd) between the groups, leaf area per leaf, leaf specific mass, chlorophyll per leaf area, incident quantum yield, leaf respiration rate, and irradiance at light compensation were lower for low-psi(pd) trees than for trees with high psi(pd). Nitrogen per leaf area did not differ between the groups. Net photosynthetic capacity at 2000 mu mol m(-2) s(-1) (A(max)) per leaf area was similar among all trees in the spring, but A(max)/leaf mass during the spring was higher for trees that eventually would develop low seasonal psi(pd). Since differences existed between new cohorts of leaves produced in the spring before summer drought, when psi(pd) was similar, we suggest that some leaf characteristics of Q. douglasii trees are determined by the de ree of drought exposure experienced in previous years, or by genetic variation within the species. During the rainless summer and fall seasons, A(max)/leaf area, A(max)/leaf mass, and total leaf chlorophyll/leaf mass decreased more rapidly in trees with low psi(pd) than in trees with high psi(pd), so that from August to the beginning of leaf senescence in October, leaves of high-psi(pd) trees had higher A(max)/leaf area, A(max)/leaf mass, and total leaf chlorophyll/leaf mass than those of low-psi(pd) trees. Overall, variations in root architecture and summer psi(pd), for Q. douglasii were correlated with substantial differences in morphological and physiological leaf characteristics. This apparent coordination of aboveground and belowground organs may explain, in part, how Q. douglasii tolerates the exceptionally broad range of topography and soil moisture conditions in which it occurs

Effects of Regional Origin and Genotype on Intraspecific Root Communication in the Desert Shrub Ambrosia Dumosa (Asteraceae)

Previous work has shown that the contact inhibition that occurs among roots of Ambrosia dumosa shrubs has a self/nonself recognition capability. In the current study, we investigated some of the geographic and genotypic dimensions of this recognition capability by using root observation chambers to observe the effects of encounters of individual roots on root elongation rates. We measured such effects in encounters between roots of plants from the same region and compared these to effects in encounters between roots of plants from two different regions. We also measured effects of encounters between roots of plants from the same clones and compared these to effects of encounters of roots of plants from different clones. Roots of plants from the same region (population) showed the usual \u27\u27nonself\u27\u27 precipitous decline in elongation rates following contact, but when roots of plants from different regions contacted each other, elongation rates continued unchanged. When roots of separate plants from the same clone contacted each other, the same \u27\u27nonself\u27\u27 precipitous decline in elongation rates as seen in encounters between roots of plants of different clones from the same region occurred. Meanwhile, in these same experiments \u27\u27self\u27\u27 contacts between sister roots connected to the same plants resulted in no changes in elongation rates. Thus, differences between individuals from two geographically separate populations of Ambrosia dumosa may be sufficient to thwart the \u27\u27nonself,\u27\u27 population-level recognition of similarity apparently necessary for contact inhibition. Furthermore, the \u27\u27self\u27\u27 recognition mechanism, which precludes contact inhibition between two roots on the same plant, appears to be physiological rather than genetic in nature

Weed-Biocontrol Insects Reduce Native-Plant Recruitment Through Second-Order Apparent Competition

Small-mammal seed predation is an important force structuring native-plant communities that may also influence exotic-plant invasions. In the intermountain West, deer mice (Peromyscus maniculatus) are prominent predators of native-plant seeds, but they avoid consuming seeds of certain widespread invasives like spotted knapweed (Centaurea maculosa). These mice also consume the biological-control insects Urophora spp. introduced to control C. maculosa, and this food resource substantially increases deer mouse populations. Thus, mice may play an important role in the invasion and management of C. maculosa through food-web interactions. We examined deer mouse seed predation and its effects on seedling emergence and establishment of a dominant native grass, Pseudoroegneria spicata, and forb, Balsamorhiza sagittata, in C. maculosa-invaded grasslands that were treated with herbicide to suppress C. maculosa or left untreated as controls. Deer mice readily took seeds of both native plants but removed 2–20 times more of the larger B. sagittata seeds than the smaller P. spicata seeds. Seed predation reduced emergence and establishment of both species but had greater impacts on B. sagittata. The intensity of seed predation corresponded with annual and seasonal changes in deer mouse abundance, suggesting that abundance largely determined mouse impacts on native-plant seeds. Accordingly, herbicide treatments that reduced mouse abundance by suppressing C. maculosa and its associated biocontrol food subsidies to mice also reduced seed predation and decreased the impact of deer mice on B. sagittata establishment. These results provide evidence that Urophora biocontrol agents may exacerbate the negative effects of C. maculosa on native plants through a form of second-order apparent competition—a biocontrol indirect effect that has not been previously documented. Herbicide suppressed C. maculosa and Urophora, reducing mouse populations and moderating seed predation on native plants, but the herbicide\u27s direct negative effects on native forb seedlings overwhelmed the indirect positive effect of reducing deer mouse seed predation. By manipulating this four-level food chain, we illustrate that host-specific biological control agents may impact nontarget plant species through food-web interactions, and herbicides may influence management outcomes through indirect trophic interactions in addition to their direct effects on plants. Read More: http://www.esajournals.org/doi/abs/10.1890/07-1789.1?journalCode=eca