Sensitivity of Surface Materials and Vegetation to Disturbance in the Queen Elizabeth Islands: An Approach and Commentary

Concern about potential and actual disturbance of surface materials, vegetation and wildlife of the Queen Elizabeth Islands has risen sharply in the last few years. The purpose of this paper is to outline an approach to the problem, based on terrain studies, and to offer a commentary on the recent paper by T.A. Babb and L.C. Bliss in Arctic. … For a rational assessment of the problem, information is required on: a) surface materials - ice content, texture, engineering properties; b) topography and landforms; c) geomorphic processes; d) drainage - seasonal change and single events; e) vegetation - percentage cover and composition by species; f) summer temperatures, and moisture balance in soil; g) wildlife. … Surface materials are very significant elements of the terrain, especially when potential for disturbance is being considered. Hence, surface materials are used by the present writers as a nucleus around which other elements of the terrain are grouped. … Two of the present writers undertook in 1972 an exercise in the mapping of sensitivity at a scale of 1:500,000 of the Queen Elizabeth Islands, based primarily on bedrock maps and extensive personal communications, but found it unsatisfactory because the degree of detail was insufficient to reflect the variability in the sensitivity of the terrain. … [In evaluating the paper by Babb and Bliss, the present authors conclude that]: The overall objective of these authors in emphasizing the "susceptibility of the soils and vegetation to surface disturbance" is good. However the methods used to achieve this objective are inconsistent, and in several cases the results are inaccurate. A serious deficiency is that the criteria for determining categories of "susceptibility" are obscure. … The "Polar Desert" category is described as an area with 10% or less plant cover, low susceptibility to disturbance and low ground ice content. One interpretation of this seems to be that poorly-vegetated areas are less susceptible to disturbance of vegetation than are more densely vegetated areas. Only in so far as a low plant density lessens the probability of direct impact of vehicles on plants is this interpretation obviously true. A sparsely vegetated area may be an important, or even critical, range for ungulates; therefore the effect of disturbance of it could be great. The type of vegetation - such as willow, sedge, saxifrage, grass or bryophyte - is a vital consideration. An alternative interpretation is that unvegetated areas (90% of the Polar Desert category, classed as "soils") have a low sensitivity to surface disturbance. This is not true for some major areas of both eastern Melville Island and Western Ellesmere Island where highly sensitive surfaces, almost devoid of vegetation, are subject to extensive slope failure or thermokarst development, even without disturbance. Where the authors have left their major field of expertise and have commented on geology and geomorphology, weaknesses are evident. They appear to draw a direct relationship between active-layer soil moisture and "susceptibility". For overland travel this is generally true, but if excavation penetrates the shallow active layer and the frost table, then the relationship certainly no longer holds. Furthermore, the implication of a relationship between susceptibility, ice content and vegetation cover is simplistic and can be misleading. The assertion that "10% or more vegetation cover indicates the existence of sufficient moisture for the segregation of horizontal ice layers" is without basis. The present writers have drilled over 300 shallow (1-6 m) holes in eastern Melville Island and western Ellesmere Island to evaluate ice content and have found the relationship between vegetation, ground ice and materials to be complex. &hellip

Smooth operator? Understanding and visualising mutation bias

The potential for mutation operators to adversely affect the behaviour of evolutionary algorithms is demonstrated for both real-valued and discrete-valued genotypes. Attention is drawn to the utility of effective visualisation techniques and explanatory concepts in identifying and understanding these biases. The skewness of a mutation distribution is identified as a crucial determinant of its bias. For redundant discrete genotype-phenotype mappings intended to exploit neutrality in genotype space, it is demonstrated that in addition to the mere extent of phenotypic connectivity achieved by these schemes, the distribution of phenotypic connectivity may be critical in determining whether neutral networks improve the ability of an evolutionary algorithm overall. Mutation operators lie at the heart of evolutionary algorithms. They corrupt the reproduction of genotypes, introducing the variety that fuels natural selection. However, until recently, the process of mutation has taken..

Scheme and Scale Dependence of Charm Production in Neutrino Scattering

We discuss some theoretical uncertainties in the calculation of the cross section for charm production in charged current deep inelastic neutrino scattering related to ambiguities in the treatment of terms which are singular in the limit of a vanishing charm mass. In particular we compare the so-called variable flavour scheme where these terms are absorbed in the parton distribution functions containing the charm as an active flavour, with the so-called fixed flavour scheme with no charm mass subtraction where the charm appears only in the final state of fixed-order scattering matrix elements. Using available parametrizations of parton distribution functions we find that the two schemes lead to largely differing results for separate structure functions whereas the differences cancel to a large extent in the total cross section in that kinematical region which has been measured so far.Comment: 20pages, uuencoded postscript, figures include

Extraction of the D13(1520) photon-decay couplings from pion- and eta-photoproduction data

We compare results for the D13(1520) photon-decay amplitudes determined in analyses of eta- and pion-photoproduction data. The ratio of helicity amplitudes (A_3/2 / A_1/2), determined from eta-photoproduction data, is quite different from that determined in previous analyses of pion-photoproduction data. We consider how strongly the existing pion-photoproduction data constrain both this ratio and the individual photon-decay amplitudes.Comment: 7 pages, 2 figure

Altered precipitation and root herbivory affect the productivity and composition of a mesic grassland

Background Climate change models predict changes in the amount, frequency and seasonality of precipitation events, all of which have the potential to affect the structure and function of grassland ecosystems. While previous studies have examined plant or herbivore responses to these perturbations, few have examined their interactions; even fewer have included belowground herbivores. Given the ecological, economic and biodiversity value of grasslands, and their importance globally for carbon storage and agriculture, this is an important knowledge gap. To address this, we conducted a precipitation manipulation experiment in a former mesic pasture grassland comprising a mixture of C-4 grasses and C-3 grasses and forbs, in southeast Australia. Rainfall treatments included a control [ambient], reduced amount [50% ambient] and reduced frequency [ambient rainfall withheld for three weeks, then applied as a single deluge event] manipulations, to simulate predicted changes in both the size and frequency of future rainfall events. In addition, half of all experimental plots were inoculated with adult root herbivores (Scarabaeidae beetles). Results We found strong seasonal dependence in plant community responses to both rainfall and root herbivore treatments. The largest effects were seen in the cool season with lower productivity, cover and diversity in rainfall-manipulated plots, while root herbivore inoculation increased the relative abundance of C-3, compared to C-4, plants. Conclusions This study highlights the importance of considering not only the seasonality of plant responses to altered rainfall, but also the important role of interactions between abiotic and biotic drivers of vegetation change when evaluating ecosystem-level responses to future shifts in climatic conditions.This work was partially supported by a Higher Degree Research Scholarship from the Hawkesbury Institute for the Environment at Western Sydney University. Additional funding came from a project grant to SAP and SNJ from the Hermon Slade Foundation (P00021516) and funding provided by Western Sydney University. The Western Sydney University Library provided financial assistance for open access publication fees. Documen

Kinetic model of II-VI(001) semiconductor surfaces: Growth rates in atomic layer epitaxy

We present a zinc-blende lattice gas model of II-VI(001) surfaces, which is investigated by means of Kinetic Monte Carlo (KMC) simulations. Anisotropic effective interactions between surface metal atoms allow for the description of, e.g., the sublimation of CdTe(001), including the reconstruction of Cd-terminated surfaces and its dependence on the substrate temperature T. Our model also includes Te-dimerization and the potential presence of excess Te in a reservoir of weakly bound atoms at the surface. We study the self-regulation of atomic layer epitaxy (ALE) and demonstrate how the interplay of the reservoir occupation with the surface kinetics results in two different regimes: at high T the growth rate is limited to 0.5 layers per ALE cycle, whereas at low enough T each cycle adds a complete layer of CdTe. The transition between the two regimes occurs at a characteristic temperature and its dependence on external parameters is studied. Comparing the temperature dependence of the ALE growth rate in our model with experimental results for CdTe we find qualitative agreement.Comment: 9 pages (REVTeX), 8 figures (EPS). Content revised, references added, typos correcte

Quantum Vacuum Instability Near Rotating Stars

We discuss the Starobinskii-Unruh process for the Kerr black hole. We show how this effect is related to the theory of squeezed states. We then consider a simple model for a highly relativistic rotating star and show that the Starobinskii-Unruh effect is absent.Comment: 17 Pages, (accepted by PRD), (previously incorrect header files have been corrected

Variational Calculations for 3^3He Impurities on 4^4He Droplets

Variational Monte Carlo method is used to calculate ground state properties of $^4$He droplets, containing 70, 112, 168, 240, 330, and 728 particles. The resulting particle and kinetic energy densities are used as an input in the Feynman-Lekner theory for $^3$He impurities. The kinetic energy density of $^4$He atoms and the energy of the $^3$He surface states are compared with the results of previous phenomenological calculations.Comment: 12 pages, in revtex 3.0, with 5 .ps figure

Evidence for the fourth P11 resonance predicted by the constituent quark model

It is pointed out that the third of five low-lying P11 states predicted by a constituent quark model can be identified with the third of four states in a solution from a three-channel analysis by the Zagreb group. This is one of the so-called ``missing'' resonances, predicted at 1880 MeV. The fit of the Zagreb group to the pi N -> eta N data is the crucial element in finding this fourth resonance in the P11 partial wave.Comment: 8 pages, revtex; expanded acknowledgement

A lattice model for the kinetics of rupture of fluid bilayer membranes

We have constructed a model for the kinetics of rupture of membranes under tension, applying physical principles relevant to lipid bilayers held together by hydrophobic interactions. The membrane is characterized by the bulk compressibility (for expansion), the thickness of the hydrophobic part of the bilayer, the hydrophobicity and a parameter characterizing the tail rigidity of the lipids. The model is a lattice model which incorporates strain relaxation, and considers the nucleation of pores at constant area, constant temperature, and constant particle number. The particle number is conserved by allowing multiple occupancy of the sites. An equilibrium ``phase diagram'' is constructed as a function of temperature and strain with the total pore surface and distribution as the order parameters. A first order rupture line is found with increasing tension, and a continuous increase in proto-pore concentration with rising temperature till instability. The model explains current results on saturated and unsaturated PC lipid bilayers and thicker artificial bilayers made of diblock copolymers. Pore size distributions are presented for various values of area expansion and temperature, and the fractal dimension of the pore edge is evaluated.Comment: 15 pages, 8 figure