662 research outputs found
Scattering in three-dimensional fuzzy space
We develop scattering theory in a non-commutative space defined by a
coordinate algebra. By introducing a positive operator valued measure as a
replacement for strong position measurements, we are able to derive explicit
expressions for the probability current, differential and total cross-sections.
We show that at low incident energies the kinematics of these expressions is
identical to that of commutative scattering theory. The consequences of spacial
non-commutativity are found to be more pronounced at the dynamical level where,
even at low incident energies, the phase shifts of the partial waves can
deviate strongly from commutative results. This is demonstrated for scattering
from a spherical well. The impact of non-commutativity on the well's spectrum
and on the properties of its bound and scattering states are considered in
detail. It is found that for sufficiently large well-depths the potential
effectively becomes repulsive and that the cross-section tends towards that of
hard sphere scattering. This can occur even at low incident energies when the
particle's wave-length inside the well becomes comparable to the
non-commutative length-scale.Comment: 12 pages, 6 figure
Spectrum of the three dimensional fuzzy well
We develop the formalism of quantum mechanics on three dimensional fuzzy
space and solve the Schr\"odinger equation for a free particle, finite and
infinite fuzzy wells. We show that all results reduce to the appropriate
commutative limits. A high energy cut-off is found for the free particle
spectrum, which also results in the modification of the high energy dispersion
relation. An ultra-violet/infra-red duality is manifest in the free particle
spectrum. The finite well also has an upper bound on the possible energy
eigenvalues. The phase shifts due to scattering around the finite fuzzy
potential well have been calculated
Species of Cercospora associated with grey leaf spot of maize
Grey leaf spot is a serious yield-reducing disease of maize (Zea
mays) in many parts of the world where this crop is cultivated. The
causal organism associated with the disease is Cercospora
zeae-maydis. Two potential sibling species have been recognized as Groups
I and II. The DNA sequences for the internal transcribed spacers (ITS1 &
ITS2), the 5.8S rRNA gene, elongation factor 1-α, histone H3, actin and
calmodulin gene regions suggest that Groups I and II are two distinct species.
Furthermore, Cercospora zeae-maydis (Group I) can be distinguished
from C. zeina sp. nov. (Group II) by its faster growth rate on
artificial media, the ability to produce cercosporin, longer conidiophores,
and broadly fusiform conidia. A PCR-based test that distinguishes the two
species was developed using species-specific primers designed from the histone
H3 gene
Eucalyptus microfungi known from culture. 1. Cladoriella and Fulvoflamma genera nova, with notes on some other poorly known taxa
A study of microfungi associated with living Eucalyptus leaves and
leaf litter revealed several novel and interesting taxa. Cladoriella
eucalypti gen. et sp. nov. is described as a Cladosporium-like
genus associated with litter collected in South Africa, while Fulvoflamma
eucalypti gen. et. sp. nov. is newly described from leaf litter collected
in Spain. Beta-conidia are newly reported for species of
Pestalotiopsis, namely Pestalotiopsis disseminata in New
Zealand, and a Pestalotiopsis sp. from Colombia. Satchmopsis
brasiliensis is reported from litter in Colombia and Indonesia, while
Torrendiella eucalypti is reported from leaf litter in Indonesia, and
shown to have a Sporothrix-like anamorph. Leptospora rubella
is reported from living Eucalyptus leaves in Colombia, where it is
associated with leaf spots of Mycosphaerella longibasalis, while
Macrohilum eucalypti is reported from leaf spots of
Eucalyptus in New Zealand
Comparison of the updated South African road safety assessment methods (sarsam 2022) with the South African road safety manual (sarsam 2012)
Papers presented virtually at the 41st International Southern African Transport Conference on 10-13 July 2023.The South African Road Safety Assessment Methods of 2022 (SARSAM 2022) replaced
the previous South African Road Safety Audit Manual of 2012 (SARSAM, 2012). The
SARSAM 2022 is part of the Technical Recommendations for Highways compiled under
auspices of the Committee of Transport Officials (COTO), TRH 29.
The Safe System Approach incorporates the principle that humans are frail and that the
human body cannot withstand the kinetic energy that is transferred if a collision occurs
without being killed or seriously injured. As such it is the responsibility of the road designer
(authority) to design a road and road environment that is inherently safe. SARSAM 2012
was updated to incorporate the Safe System principles.
The updated document now consists of three volumes which deals with Road Network
Screening, Road Safety Inspections and Road Safety Audits. The accreditation of auditors
by Engineering Council of South Africa (ECSA) has progressed and has now been
incorporated in the updated methods.
This paper highlights the substantial changes that occurred with the updated documen
Re-evaluating the taxonomic status of Phaeoisariopsis griseola, the causal agent of angular leaf spot of bean
Angular leaf spot of Phaseolus vulgaris is a serious disease
caused by Phaeoisariopsis griseola, in which two major gene pools
occur, namely Andean and Middle-American. Sequence analysis of the SSU region
of nrDNA revealed the genus Phaeoisariopsis to be indistinguishable
from other hyphomycete anamorph genera associated with
Mycosphaerella, namely Pseudocercospora and
Stigmina. A new combination is therefore proposed in the genus
Pseudocercospora, a name to be conserved over
Phaeoisariopsis and Stigmina. Further comparisons by means
of morphology, cultural characteristics, and DNA sequence analysis of the ITS,
calmodulin, and actin gene regions delineated two groups within P.
griseola, which are recognised as two formae, namely f. griseola
and f. mesoamericana
Cylindrocarpon root rot: multi-gene analysis reveals novel species within the Ilyonectria radicicola species complex
Abstract Ilyonectria radicicola and its Cylindrocarpon-like
anamorph represent a species complex that is commonly
associated with root rot disease symptoms on a range of
hosts. During the course of this study, several species could
be distinguished from I. radicicola sensu stricto based on
morphological and culture characteristics. DNA sequence
analysis of the partial β-tubulin, histone H3, translation
elongation factor 1-α and nuclear ribosomal RNA-Internal
Transcribed Spacer (nrRNA-ITS) genes were employed to
provide further support for the morphological species
resolved among 68 isolates associated with root rot disease
symptoms. Of the various loci screened, nrRNA-ITS
sequences were the least informative, while histone H3
sequences were the most informative, resolving the same
number of species as the combined dataset across the four
genes. Within the Ilyonectria radicicola species complex,
12 new taxa are delineated occurring on a diverse range of hosts, the most common being Cyclamen, Lilium, Panax,
Pseudotsuga, Quercus and Vitis
Relativistic mean field formulation of clustering in heavy nuclei
Very little is known about clustering in heavy nuclei and in particular the
interaction between the correlated cluster nucleons and remaining core nucleons. Currently
the phenomenological Saxon-Woods plus cubic Saxon-Woods core-cluster potential successfully
predicts the alpha decay half-life and energy band spectra of a number of heavy nuclei. This
model, however, lacks a microscopic understanding of clustering phenomenon in these heavy
nuclear systems. A fully relativistic microscopic formalism is presented, which generates the
core-cluster potential by means of the McNeil, Ray and Wallace based double folding procedure.
The core and cluster baryon densities are calculated by using a relativistic mean field approach.
The Lorentz covariant IA1 representation of the nucleon-nucleon interaction is folded with the
core and cluster densities. Theoretical predictions of the ground-state decay half-life and positive
parity energy band of 212Po are obtained with the relativistic mean field formalism and which
are compared to the results from the phenomenological Saxon-Woods plus cubic Saxon-Wood
core-cluster potential and microscopic M3Y interaction
What is Johansonia?
The bitunicate ascomycete genus Johansonia is presently treated as a member of Saccardiaceae, a family regarded as incertae sedis within the Ascomycota. Recent collections on leaves of a leguminous host, Dimorphandra
mollis, in Mato Grosso, Brazil, led to the discovery of a new species of Johansonia, described here as J.
chapadiensis. Based on DNA sequence data of the nuclear ribosomal DNA (LSU), Johansonia is revealed to represent a member of Dothideomycetes, Capnodiales. Although its family could not be resolved, it clustered basal to Schizothyriaceae and Mycosphaerellaceae, and could well represent a species of Saccardiaceae. DNA sequence data of other members of Saccardiaceae would be required, however, to confirm this classification
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