The influence of edge effects on evapotranspiration of fragmented woodlands. Der Einfluss von Randeffekten auf die Verdunstung fragmentierter Waldbestande

The water use of forests has been the subject of many studies in the past decades. They were mostly carried out in extensive areas of woodland and achieved consistent results. However, there is as yet a large uncertainty about the role of fragmented woodlands in the catchment water balance, since water losses from small patches of woodland have rarely been measured. In the framework of the "Lowland Catchment Research" (LOCAR) programme, a 7-months field measurement campaign has been carried out in southern England in order to measure the transpiration of a mixed deciduous forest in various distances from the forest edge by means of the sap flux techniqure. The annual transpiration per unit ground area near the forest edge equalled potential evaporation and was about 60% higher than in the forest interior and similar to the transpiration of hedgerows as determined in a corresponding study. Interception evaporation was not affected by the proximity to an edge. Based on these results it is shown that the edge effect dominates the water use of small forests (<10 ha) and becomes negligible only for woodlands larger than 100 ha

Representing First-Order Logic Using Graphs

Abstract. We show how edge-labelled graphs can be used to represent first-order logic formulae. This gives rise to recursively nested structures, in which each level of nesting corresponds to the negation of a set of existentials. The model is a direct generalisation of the negative application conditions used in graph rewriting, which count a single level of nesting and are thereby shown to correspond to the fragment ∃¬∃ of first-order logic. Vice versa, this generalisation may be used to strengthen the notion of application conditions. We then proceed to show how these nested models may be flattened to (sets of) plain graphs, by allowing some structure on the labels. The resulting formulae-as-graphs may form the basis of a unification of the theories of graph transformation and predicate transformation

Transverse oscillations of coronal loops

On 14 July 1998 TRACE observed transverse oscillations of a coronal loop generated by an external disturbance most probably caused by a solar flare. These oscillations were interpreted as standing fast kink waves in a magnetic flux tube. Firstly, in this review we embark on the discussion of the theory of waves and oscillations in a homogeneous straight magnetic cylinder with the particular emphasis on fast kink waves. Next, we consider the effects of stratification, loop expansion, loop curvature, non-circular cross-section, loop shape and magnetic twist. An important property of observed transverse coronal loop oscillations is their fast damping. We briefly review the different mechanisms suggested for explaining the rapid damping phenomenon. After that we concentrate on damping due to resonant absorption. We describe the latest analytical results obtained with the use of thin transition layer approximation, and then compare these results with numerical findings obtained for arbitrary density variation inside the flux tube. Very often collective oscillations of an array of coronal magnetic loops are observed. It is natural to start studying this phenomenon from the system of two coronal loops. We describe very recent analytical and numerical results of studying collective oscillations of two parallel homogeneous coronal loops. The implication of the theoretical results for coronal seismology is briefly discussed. We describe the estimates of magnetic field magnitude obtained from the observed fundamental frequency of oscillations, and the estimates of the coronal scale height obtained using the simultaneous observations of the fundamental frequency and the frequency of the first overtone of kink oscillations. In the last part of the review we summarise the most outstanding and acute problems in the theory of the coronal loop transverse oscillations

Infrared Behaviour of The Gluon Propagator in Non-Equilibrium Situations

The infrared behaviour of the medium modified gluon propagator in non-equilibrium situations is studied in the covariant gauge using the Schwinger-Keldysh closed-time path formalism. It is shown that the magnetic screening mass is non-zero at the one loop level whenever the initial gluon distribution function is non isotropic with the assumption that the distribution function of the gluon is not divergent at zero transverse momentum. For isotropic gluon distribution functions, such as those describing local equilibrium, the magnetic mass at one loop level is zero which is consistent with finite temperature field theory results. Assuming that a reasonable initial gluon distribution function can be obtained from a perturbative QCD calculation of minijets, we determine these out of equilibrium values for the initial magnetic and Debye screening masses at energy densities appropriate to RHIC and LHC. We also compare the magnetic masses obtained here with those obtained using finite temperature lattice QCD methods at similar temperatures at RHIC and LHC.Comment: 21 pages latex, 4 figures, final version to be published in Phys. Rev.

Closed-Time Path Integral Formalism and Medium Effects of Non-Equilibrium QCD Matter

We apply the closed-time path integral formalism to study the medium effects of non-equilibrium gluon matter. We derive the medium modified resummed gluon propagator to the one loop level in non-equilibrium in the covariant gauge. The gluon propagator we derive can be used to remove the infrared divergences in the secondary parton collisions to study thermalization of minijet parton plasma at RHIC and LHC.Comment: Final version, To appear in Physical Review D, Minor modification, reference adde

Antibiotics in agroecosystems: Introduction to the special section

The presence of antibiotic drug residues, antibiotic resistant bacteria, and antibiotic resistance genes in agroecosystems has become a significant area of research in recent years, and is a growing public health concern. While antibiotics are utilized for human medicine and agricultural practices, the majority of antibiotic use occurs in food animals where these drugs have historically been used for growth promotion, in addition to prevention and treatment of disease. The widespread use of antibiotics combined with the application of human and animal wastes to agricultural fields introduces antibiotic-related contamination into the environment. While overt toxicity in organisms directly exposed to antibiotic in agroecosystems is generally not an issue due to concentrations generally lower than therapeutic doses, the impacts of introducing antibiotic contaminants are unknown, and concerns have arisen about the health of humans, animals and ecosystems (One Health). Despite increases in research focused on the fate and occurrence of antibiotics and antibiotic resistance over the past decade, standard methodologies and practices for analyzing environmental samples are limited, and future research needs are becoming evident. To address these issues in detail, this special section was developed with a framework of five core review papers that address the (i) overall state of science of antibiotics and antibiotic resistance in agroecosystems with a causal model; (ii) chemical analysis of antibiotics in the environment; (iii) necessity for background and baseline data for studies of antibiotic resistance in agroecosystems with a decision-making tool to assist in designing research studies; as well as (iv) culture- and (v) molecular-based methods for analyzing antibiotic resistance in the environment. With a focus on the core review papers, this introduction to the special section summarizes the current state of science for analyzing antibiotics and antibiotic resistance in agroecosystems, while also discussing current knowledge gaps and future research priorities. This introduction also contains a glossary of terminologies that are commonly used throughout the special section. By defining these terminologies, it is hoped to provide a common language that clearly defines the linkages across the narratives of each paper

Current status of turbulent dynamo theory: From large-scale to small-scale dynamos

Several recent advances in turbulent dynamo theory are reviewed. High resolution simulations of small-scale and large-scale dynamo action in periodic domains are compared with each other and contrasted with similar results at low magnetic Prandtl numbers. It is argued that all the different cases show similarities at intermediate length scales. On the other hand, in the presence of helicity of the turbulence, power develops on large scales, which is not present in non-helical small-scale turbulent dynamos. At small length scales, differences occur in connection with the dissipation cutoff scales associated with the respective value of the magnetic Prandtl number. These differences are found to be independent of whether or not there is large-scale dynamo action. However, large-scale dynamos in homogeneous systems are shown to suffer from resistive slow-down even at intermediate length scales. The results from simulations are connected to mean field theory and its applications. Recent work on helicity fluxes to alleviate large-scale dynamo quenching, shear dynamos, nonlocal effects and magnetic structures from strong density stratification are highlighted. Several insights which arise from analytic considerations of small-scale dynamos are discussed.Comment: 36 pages, 11 figures, Spa. Sci. Rev., submitted to the special issue "Magnetism in the Universe" (ed. A. Balogh