1,424 research outputs found
Two new pathogenic ascomycetes in Guignardia and Rosenscheldiella on New Zealand's pygmy mistletoes (Korthalsella: Viscaceae)
Two new pathogens, Guignardia korthalsellae and
Rosenscheldiella korthalsellae, are described from New Zealand's
pygmy mistletoes (Korthalsella, Viscaceae). Both form
ascomata on living phylloclades with minimal disruption of the tissue. Fungal
hyphae within the phylloclade are primarily intercellular. Guignardia
korthalsellae disrupts a limited number of epidermal cells immediately
around the erumpent ascoma, while the ascomata of Rosenscheldiella
korthalsellae develop externally on small patches of stromatic tissue
that form above stomatal cavities. Rosenscheldiella is applied in a
purely morphological sense. LSU sequences show that R. korthalsellae
as well as another New Zealand species, Rosenscheldiella
brachyglottidis, are members of the Mycosphaerellaceae sensu
stricto. Genetically, Rosenscheldiella, in the sense we are
using it, is polyphyletic; LSU and ITS sequences place the two New Zealand
species in different clades within the Mycosphaerellaceae.
Rosenscheldiella is retained for these fungi until generic
relationships within the family are resolved. Whether or not the type species
of Rosenscheldiella, R. styracis, is also a member of the
Mycosphaerellaceae is not known, but it has a similar morphology and
relationship to its host as the two New Zealand species
What can mathematical models bring to the control of equine influenza?
Mathematical modelling of infectious disease is increasingly regarded as an important tool in the development of disease prevention and control measures. This article brings together key findings from various modelling studies conducted over the past 10 years that are of relevance to those on the front line of the battle against equine influenza
Computational modelling and experimental characterisation of heterogeneous materials
Heterogeneous materials can exhibit behaviour under load that cannot be described by classical continuum elasticity. Beams in bending can show a relative stiffening as the beam depth tends to zero, a size effect. Size effects are recognised in higher order continuum elastic theories such as micropolar elasticity. The drawback of higher order theories is the requirement of addition constitutive relations and associated properties that are often difficult to establish experimentally. Furthermore the finite element method, of great benefit in classical elasticity, has shown limitations when applied to micropolar elasticity. The determination of additional constitutive properties and the computational modelling of micropolar elasticity will be discussed in the context of a model heterogeneous material loaded in simple 3 point bending. The model material was created by drilling holes in aluminium bar in a regular pattern, with the hole axis normal to the plane of bending. The bending tests show that a size effect is present. These results are compared against modelling the detailed beam geometries in the finite element package ANSYS, which again shows the size effect. These two bending test are used to extract the additional micropolar elastic material properties. A comparison is then made against analytical solutions,numerical solutions using a micropolar beam finite element and a micropolar plane stress control volume method.It will be shown that the need for extensive experimental testing to determine the additional constitutive properties may not be necessary with the appropriate use of numerical methods
Classical tests of general relativity in the Newtonian limit of Schwarzschild-de Sitter spacetime
Recently it has been shown that despite previous claims the cosmological
constant affects light bending. In the present article we study light bending
and the advance of Mercury's perihelion in the context of the Newtonian limit
of Schwarzschild-de Sitter spacetime employing the special relativistic
equivalence of mass and energy. In both cases, up to a constant factor, we find
the same results as in the full general relativistic treatment of the same
phenomena. These approximate and intuitive arguments demonstrate clearly what
effects should have been expected from the presence of in the general
relativistic treatment of these phenomena.Comment: 12 pages, Revtex, 1 figur
Revised Phase Diagram of the Gross-Neveu Model
We confirm earlier hints that the conventional phase diagram of the discrete
chiral Gross-Neveu model in the large N limit is deficient at non-zero chemical
potential. We present the corrected phase diagram constructed in mean field
theory. It has three different phases, including a kink-antikink crystal phase.
All transitions are second order. The driving mechanism for the new structure
of baryonic matter in the Gross-Neveu model is an Overhauser type instability
with gap formation at the Fermi surface.Comment: Revtex, 12 pages, 15 figures; v2: Axis labelling in Fig. 9 correcte
What can mathematical models bring to the control of equine influenza?
Mathematical modelling of infectious disease is increasingly regarded as an important tool in the development of disease prevention and control measures. This article brings together key findings from various modelling studies conducted over the past 10 years that are of relevance to those on the front line of the battle against equine influenza
Directed geometrical worm algorithm applied to the quantum rotor model
We discuss the implementation of a directed geometrical worm algorithm for
the study of quantum link-current models. In this algorithm Monte Carlo updates
are made through the biased reptation of a worm through the lattice. A directed
algorithm is an algorithm where, during the construction of the worm, the
probability for erasing the immediately preceding part of the worm, when adding
a new part,is minimal. We introduce a simple numerical procedure for minimizing
this probability. The procedure only depends on appropriately defined local
probabilities and should be generally applicable. Furthermore we show how
correlation functions, C(r,tau) can be straightforwardly obtained from the
probability of a worm to reach a site (r,tau) away from its starting point
independent of whether or not a directed version of the algorithm is used.
Detailed analytical proofs of the validity of the Monte Carlo algorithms are
presented for both the directed and un-directed geometrical worm algorithms.
Results for auto-correlation times and Green functions are presented for the
quantum rotor model.Comment: 11 pages, 9 figures, v2 : Additional results and data calculated at
an incorrect chemical potential replaced. Conclusions unchange
Bulk-sensitive photoemission spectroscopy of A_2FeMoO_6 double perovskites (A=Sr, Ba)
Electronic structures of Sr_2FeMoO_6 (SFMO) and Ba_2FeMoO_6 (BFMO) double
perovskites have been investigated using the Fe 2p->3d resonant photoemission
spectroscopy (PES) and the Cooper minimum in the Mo 4d photoionization cross
section. The states close to the Fermi level are found to have strongly mixed
Mo-Fe t_{2g} character, suggesting that the Fe valence is far from pure 3+. The
Fe 2p_{3/2} XAS spectra indicate the mixed-valent Fe^{3+}-Fe^{2+}
configurations, and the larger Fe^{2+} component for BFMO than for SFMO,
suggesting a kind of double exchange interaction. The valence-band PES spectra
reveal good agreement with the LSDA+U calculation.Comment: 4 pages, 3 figure
Backward pion-nucleon scattering
A global analysis of the world data on differential cross sections and
polarization asymmetries of backward pion-nucleon scattering for invariant
collision energies above 3 GeV is performed in a Regge model. Including the
, , and trajectories, we
reproduce both angular distributions and polarization data for small values of
the Mandelstam variable , in contrast to previous analyses. The model
amplitude is used to obtain evidence for baryon resonances with mass below 3
GeV. Our analysis suggests a resonance with a mass of 2.83 GeV as
member of the trajectory from the corresponding Chew-Frautschi
plot.Comment: 12 pages, 16 figure
Frustration and the Kondo effect in heavy fermion materials
The observation of a separation between the antiferromagnetic phase boundary
and the small-large Fermi surface transition in recent experiments has led to
the proposal that frustration is an important additional tuning parameter in
the Kondo lattice model of heavy fermion materials. The introduction of a Kondo
(K) and a frustration (Q) axis into the phase diagram permits us to discuss the
physics of heavy fermion materials in a broader perspective. The current
experimental situation is analysed in the context of this combined "QK" phase
diagram. We discuss various theoretical models for the frustrated Kondo
lattice, using general arguments to characterize the nature of the -electron
localization transition that occurs between the spin liquid and heavy Fermi
liquid ground-states. We concentrate in particular on the Shastry--Sutherland
Kondo lattice model, for which we establish the qualitative phase diagram using
strong coupling arguments and the large- expansion. The paper closes with
some brief remarks on promising future theoretical directions.Comment: To appear in a special issue of JLT
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