2,670 research outputs found
Primordia initiation of mushroom (Agaricus bisporus) strains on axenic casing materials
The mushroom (Agaricus bisporus) has a
requirement for a ‘‘casing layer’’ that has specific
physical, chemical and microbiological properties
which stimulate and promote the initiation of primordia.
Some of these primordia then may develop
further into sporophores, involving differentiation of
tissue. Wild and commercial strains of A. bisporus
were cultured in axenic and nonaxenic microcosms,
using a rye grain substrate covered by a range of organic
and inorganic casing materials. In axenic culture,
A. bisporus (commercial strain A15) was capable
of producing primordia and mature sporophores on
charcoal (wood and activated), anthracite coal, lignite
and zeolite, but not on bark, coir, peat, rockwool,
silica or vermiculite. Of six strains tested, only
the developmental variant mutant, B430, produced
rudimentary primordia on axenic peat-based casing
material. However, none of these rudimentary primordia
developed differentiated tissues or beyond 4
mm diameter, either on axenic casing material in the
microcosms or in larger-scale culture. In larger-scale,
nonaxenic culture, strain B430 produced severely
malformed but mature sporophores in similar numbers
to those of other strains. Typically, 3–6% of primordia
developed into mature sporophores, but significant
differences in this proportion, as well as in
the numbers of primordia produced, were recorded
between 12 A. bisporus strains
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General Electric Atomic Power Equipment Department Report GEAP-4566
Quarterly report describing progress on the EVESR Nuclear Superheat Fuel Development Project
Effect of Wavefunction Renormalisation in N-Flavour Qed3 at Finite Temperature
A recent study of dynamical chiral symmetry breaking in N-flavour QED at
finite temperature is extended to include the effect of fermion wavefunction
renormalisation in the Schwinger-Dyson equations. The simple ``zero-frequency''
truncation previously used is found to lead to unphysical results, especially
as . A modified set of equations is proposed, whose solutions behave
in a way which is qualitatively similar to the solutions of Pennington et
al. [5-8] who have made extensive studies of the effect of wavefunction
renormalisation in this context, and who concluded that there was no critical
(at T=0) above which chiral symmetry was restored. In contrast, we find
that our modified equations predict a critical at , and an
phase diagram very similar to the earlier study neglecting wavefunction
renormalisation. The reason for the difference is traced to the different
infrared behaviour of the vacuum polarisation at and at .Comment: 17 pages + 13 figures (available upon request), Oxford preprint
OUTP-93-30P, IFUNAM preprint FT94-39, LaTe
String Theory and Water Waves
We uncover a remarkable role that an infinite hierarchy of non-linear
differential equations plays in organizing and connecting certain {hat c}<1
string theories non-perturbatively. We are able to embed the type 0A and 0B
(A,A) minimal string theories into this single framework. The string theories
arise as special limits of a rich system of equations underpinned by an
integrable system known as the dispersive water wave hierarchy. We observe that
there are several other string-like limits of the system, and conjecture that
some of them are type IIA and IIB (A,D) minimal string backgrounds. We explain
how these and several string-like special points arise and are connected. In
some cases, the framework endows the theories with a non-perturbative
definition for the first time. Notably, we discover that the Painleve IV
equation plays a key role in organizing the string theory physics, joining its
siblings, Painleve I and II, whose roles have previously been identified in
this minimal string context.Comment: 49 pages, 4 figure
2+1 Dimensional QED and a Novel Phase Transition
We investigate the chiral phase transition in 2+1 dimensional QED. Previous
gap equation and lattice Monte-Carlo studies of symmetry breaking have found
that symmetry breaking ceases to occur when the number of fermion flavors
exceeds a critical value. Here we focus on the order of the transition. We find
that there are no light scalar degrees of freedom present as the critical
number of flavors is approached from above (in the symmetric phase). Thus the
phase transition is not second order, rendering irrelevant the renormalization
group arguments for a fluctuation induced transition. However, the order
parameter vanishes continuously in the broken phase, so this transition is also
unlike a conventional first order phase transition.Comment: 11 pages, Late
Observation of the Higgs Boson of strong interaction via Compton scattering by the nucleon
It is shown that the Quark-Level Linear Model (QLLM) leads
to a prediction for the diamagnetic term of the polarizabilities of the nucleon
which is in excellent agreement with the experimental data. The bare mass of
the meson is predicted to be MeV and the two-photon
width keV. It is argued that the
mass predicted by the QLLM corresponds to the reaction, i.e. to a -channel pole of the reaction.
Large -angle Compton scattering experiments revealing effects of the
meson in the differential cross section are discussed. Arguments are presented
that these findings may be understood as an observation of the Higgs boson of
strong interaction while being part of the constituent quark.Comment: 17 pages, 6 figure
Non-trivial Infrared Structure in (2+1)-dimensional Quantum Electrodynamics
We show that the gauge-fermion interaction in multiflavour
-dimensional quantum electrodynamics with a finite infrared cut-off is
responsible for non-fermi liquid behaviour in the infrared, in the sense of
leading to the existence of a non-trivial fixed point at zero momentum, as well
as to a significant slowing down of the running of the coupling at intermediate
scales as compared with previous analyses on the subject. Both these features
constitute deviations from fermi-liquid theory. Our discussion is based on the
leading- resummed solution for the wave-function renormalization of the
Schwinger-Dyson equations . The present work completes and confirms the
expectations of an earlier work by two of the authors (I.J.R.A. and N.E.M.) on
the non-trivial infrared structure of the theory.Comment: 10 pages (LaTex), 5 figures (Postscript
Effect of retardation on dynamical mass generation in two-dimensional QED at finite temperature
The effect of retardation on dynamical mass generation in is studied, in the
imaginary time formalism. The photon porarization tensor is evaluated to
leading order in 1/N (N is the number of flavours), and simple closed form
expressions are found for the fully retarded longitudinal and transverse
propagators, which have the correct limit when T goes to zero. The resulting
S-D equation for the fermion mass (at order 1/N) has an infrared divergence
associated with the contribution of the transverse photon propagator; only the
longitudinal contribution is retained, as in earlier treatments. For solutions
of constant mass, it is found that the retardation reduces the value of the
parameter r (the ratio of twice the mass to the critical temperature) from
about 10 to about 6. The gap equation is then solved allowing for the mass to
depend on frequency. It was found that the r value remained close to 6.
Possibilities for including the transverse propagator are discussed.Comment: 26 pages 8 figure
Delimiting floristic biogeographic districts in the Cerrado and assessing their conservation status
This is the author accepted manuscript. The final version is available from Springer via the DOI in this recordThe Cerrado is a biodiversity hotspot in central Brazil that represents the largest
expanse of savanna in the Neotropics. Here, we aim to identify and delimit
biogeographic districts within the Cerrado, to provide a geographic framework for
conservation planning and scientific research prioritisation. We used data from 588 sites
with tree species inventories distributed across the entire Cerrado. To identify districts,
we clustered sites based on their similarity in tree species composition. To investigate
why districts differ in composition, we 1) determined the proportion of tree species in
different districts that derive from other biomes, to assess the influence of neighbouring
biomes upon geographically marginal districts and 2) assayed key climatic differences
between districts, to test the effect of environmental factors upon compositional
differences. We found seven biogeographic districts within the Cerrado. Marginal
districts have a large proportion of tree species characteristic of Amazonia and Atlantic
Forest, but the Cerrado endemic species are also important. Further, districts differed
significantly for multiple climatic variables. Finally, to provide a preliminary
conservation assessment of the different districts, we assessed their rate of land
conversion and current coverage by protected areas. We found that districts in the south
and southwest of the Cerrado have experienced the greatest land conversion and are the
least protected, while those in the north and northeast are less impacted and better
protected. Overall, our results show how biogeographic analyses can contribute to
conservation planning by giving clear guidelines on which districts merit greater
conservation and management attention.Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorConselho Nacional de Desenvolvimento Científico e Tecnológic
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