2,900 research outputs found
Breeding Ecology and Productivity of Red-Necked Grebes in Turtle Mountain Provincial Park, Manitoba
The breeding biology and productivity of the Red-necked Grebe (Podiceps grisegena) were studied in Turtle Mountain Provincial Park, Manitoba, during 1980 and 1981. Arrival dates ranged from mid-April to early June. Pre-nesting intervals ranged from 11 o 42 days and averaged about 20 days. Egg-laying commenced in early May and extended until mid-July. The average clutch size (4.95 eggs) was much larger than those found in other studies of the Red-necked Grebe in North America.
Although the nest success rate was low (26.2%), most failed pairs (83.5%) initiated at least 1 replacement clutch, and more than one-half of the observed pairs successfully hatched 1 or more chicks. Predators, primarily the Raccoon (Procyon lotor), were believed responsible for about half of the egg losses. High residue levels of several pesticides, particularly DDE and PCBs, were believed to have contributed to the low nesting success. About one-quarter of the viability-tested eggs during this study were considered inviable. Ratcliffe indices revealed that thin-shelled eggs were produced and several cracked eggs were found.
Average incubation periods calculated during this study (28-29 days) were longer than the 22-23 day incubation period generally recognized in the literature. Hatching occurred throughout June and July. Successful pairs hatched an average of 2.5 young, but raised only 1.9 young to the age of 1 month. High pesticide loads may have contributed to many of the losses that occurred during pre- and post-hatching stages. Later, intraspecific aggression probably contributed to significant differences in individual mortality rates within large and small broods. Because losses during the second month were minimal, Red-necked Grebes during this study fledged 1.8-1.9 young/successful pair or about 0.9 young/breeding pair
The microscopic nature of localization in the quantum Hall effect
The quantum Hall effect arises from the interplay between localized and
extended states that form when electrons, confined to two dimensions, are
subject to a perpendicular magnetic field. The effect involves exact
quantization of all the electronic transport properties due to particle
localization. In the conventional theory of the quantum Hall effect,
strong-field localization is associated with a single-particle drift motion of
electrons along contours of constant disorder potential. Transport experiments
that probe the extended states in the transition regions between quantum Hall
phases have been used to test both the theory and its implications for quantum
Hall phase transitions. Although several experiments on highly disordered
samples have affirmed the validity of the single-particle picture, other
experiments and some recent theories have found deviations from the predicted
universal behaviour. Here we use a scanning single-electron transistor to probe
the individual localized states, which we find to be strikingly different from
the predictions of single-particle theory. The states are mainly determined by
Coulomb interactions, and appear only when quantization of kinetic energy
limits the screening ability of electrons. We conclude that the quantum Hall
effect has a greater diversity of regimes and phase transitions than predicted
by the single-particle framework. Our experiments suggest a unified picture of
localization in which the single-particle model is valid only in the limit of
strong disorder
Evaluator services for optimised service placement in distributed heterogeneous cloud infrastructures
Optimal placement of demanding real-time interactive applications in a distributed heterogeneous cloud very quickly results in a complex tradeoff between the application constraints and resource capabilities. This requires very detailed information of the various requirements and capabilities of the applications and available resources. In this paper, we present a mathematical model for the service optimization problem and study the concept of evaluator services as a flexible and efficient solution for this complex problem. An evaluator service is a service probe that is deployed in particular runtime environments to assess the feasibility and cost-effectiveness of deploying a specific application in such environment. We discuss how this concept can be incorporated in a general framework such as the FUSION architecture and discuss the key benefits and tradeoffs for doing evaluator-based optimal service placement in widely distributed heterogeneous cloud environments
Novel metallic and insulating states at a bent quantum Hall junction
A non-planar geometry for the quantum Hall (QH) effect is studied, whereby
two quantum Hall (QH) systems are joined at a sharp right angle. When both
facets are at equal filling factor nu the junction hosts a channel with
non-quantized conductance, dependent on nu. The state is metallic at nu = 1/3,
with conductance along the junction increasing as the temperature T drops. At
nu = 1, 2 it is strongly insulating, and at nu = 3, 4 shows only weak T
dependence. Upon applying a dc voltage bias along the junction, the
differential conductance again shows three different behaviors. Hartree
calculations of the dispersion at the junction illustrate possible
explanations, and differences from planar QH structures are highlighted.Comment: 5 pages, 4 figures, text + figs revised for clarit
Quantum Hall Effect in a Two-Dimensional Electron System Bent by 90 Degrees
Using a new MBE growth technique, we fabricate a two-dimensional electron
system which is bent around an atomically sharp 90 degree corner. In the
quantum Hall regime under tilted magnetic fields, we can measure equilibration
between both co- and counter-propagating edge channels of arbitrary filling
factor ratio. We present here 4-point magnetotransport characterization of the
corner junction with filling factor combinations which can all be explained
using the standard Landauer-Buttiker edge channel picture. The success of this
description confirms the realization of a new type of quantum Hall edge
geometry.Comment: 4 pages, figures included Typographical errors corrected, reference
adde
Inference of the genetic network regulating lateral root initiation in Arabidopsis thaliana
Regulation of gene expression is crucial for organism growth, and it is one of the challenges in Systems Biology to reconstruct the underlying regulatory biological networks from transcriptomic data. The formation of lateral roots in Arabidopsis thaliana is stimulated by a cascade of regulators of which only the interactions of its initial elements have been identified. Using simulated gene expression data with known network topology, we compare the performance of inference algorithms, based on different approaches, for which ready-to-use software is available. We show that their performance improves with the network size and the inclusion of mutants. We then analyse two sets of genes, whose activity is likely to be relevant to lateral root initiation in Arabidopsis, by integrating sequence analysis with the intersection of the results of the best performing methods on time series and mutants to infer their regulatory network. The methods applied capture known interactions between genes that are candidate regulators at early stages of development. The network inferred from genes significantly expressed during lateral root formation exhibits distinct scale-free, small world and hierarchical properties and the nodes with a high out-degree may warrant further investigation
Composite fermions in periodic and random antidot lattices
The longitudinal and Hall magnetoresistance of random and periodic arrays of artificial scatterers, imposed on a high-mobility two-dimensional electron gas, were investigated in the vicinity of Landau level filling factor ν=1/2. In periodic arrays, commensurability effects between the period of the antidot array and the cyclotron radius of composite fermions are observed. In addition, the Hall resistance shows a deviation from the anticipated linear dependence, reminiscent of quenching around zero magnetic field. Both effects are absent for random antidot lattices. The relative amplitude of the geometric resonances for opposite signs of the effective magnetic field and its dependence on illumination illustrate enhanced soft wall effects for composite fermions
Classification of Higher Dimensional Spacetimes
We algebraically classify some higher dimensional spacetimes, including a
number of vacuum solutions of the Einstein field equations which can represent
higher dimensional black holes. We discuss some consequences of this work.Comment: 16 pages, 1 Tabl
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