1,360 research outputs found
Evolution of asexual and sexual reproduction in the aspergilli
Aspergillus nidulans has long-been used as a model organism to gain insights into the genetic basis of asexual and sexual developmental processes both in
other members of the genus Aspergillus, and filamentous fungi in general. Paradigms have been established concerning the regulatory mechanisms of conidial
development. However, recent studies have shown considerable genome divergence in the fungal kingdom, questioning the general applicability of findings from
Aspergillus, and certain longstanding evolutionary theories have been questioned. The phylogenetic distribution of key regulatory elements of asexual reproduction in
A. nidulans was investigated in a broad taxonomic range of fungi. This revealed that some proteins were well conserved in the Pezizomycotina (e.g. AbaA, FlbA, FluG,
NsdD, MedA, and some velvet proteins), suggesting similar developmental roles. However, other elements (e.g. BrlA) had a more restricted distribution solely in the
Eurotiomycetes, and it appears that the genetic control of sporulation seems to be more complex in the aspergilli than in some other taxonomic groups of the
Pezizomycotina. The evolution of the velvet protein family is discussed based on the history of expansion and contraction events in the early divergent fungi. Heterologous expression of the A. nidulans abaA gene in Monascus ruber failed to induce development of complete conidiophores as seen in the aspergilli, but did result in
increased conidial production. The absence of many components of the asexual developmental pathway from members of the Saccharomycotina supports the hypothesis
that differences in the complexity of their spore formation is due in part to the increased diversity of the sporulation machinery evident in the Pezizomycotina. Investigations were also made into the evolution of sex and sexuality in the aspergilli. MAT loci were identified from the heterothallic Aspergillus (Emericella) heterothallicus
and Aspergillus (Neosartorya) fennelliae and the homothallic Aspergillus pseudoglaucus (=Eurotium repens). A consistent architecture of the MAT locus was seen in
these and other heterothallic aspergilli whereas much variation was seen in the arrangement of MAT loci in homothallic aspergilli. This suggested that it is most likely that
the common ancestor of the aspergilli exhibited a heterothallic breeding system. Finally, the supposed prevalence of asexuality in the aspergilli was examined. Investigations were made using A. clavatus as a representative ‘asexual’ species. It was possible to induce a sexual cycle in A. clavatus given the correct MAT1-1 and
MAT1-2 partners and environmental conditions, with recombination confirmed utilising molecular markers. This indicated that sexual reproduction might be possible in
many supposedly asexual aspergilli and beyond, providing general insights into the nature of asexuality in fungi.National Natural Science Foundation of China 31601446National Research Foundation of Korea 2016010945Intelligent Synthetic Biology Center of Global Frontier Projects 2015M3A6A8065838Biotechnology and Biological Sciences Research CouncilGovernment of IraqMinisterio de Economía y Competitividad BIO2015-67148-
Fermion Zero Modes in the Presence of Fluxes and a Non-perturbative Superpotential
We study the effect of background fluxes of general Hodge type on the
supersymmetry conditions and on the fermionic zero modes on the world-volume of
a Euclidean M5/D3-brane in M-theory/type IIB string theory.
Using the naive susy variation of the modulino fields to determine the number
of zero modes in the presence of a flux of general Hodge type, an inconsistency
appears. This inconsistency is resolved by a modification of the supersymmetry
variation of the modulinos, which captures the back-reaction of the
non-perturbative effects on the background flux and the geometry.Comment: 21 pages, revised version contains a new appendix on dimensional
reduction of spinors and some changes in the spinor equation
High-resolution x-ray study of the nematic - smectic-A and smectic-A - smectic-C transitions in 8barS5-aerosil gels
The effects of dispersed aerosil nanoparticles on two of the phase
transitions of the thermotropic liquid crystal material
4-n-pentylphenylthiol-4'-n-octyloxybenzoate 8barS5 have been studied using
high-resolution x-ray diffraction techniques. The aerosils hydrogen bond
together to form a gel which imposes a weak quenched disorder on the liquid
crystal. The smectic-A fluctuations are well characterized by a two-component
line shape representing thermal and random-field contributions. An elaboration
on this line shape is required to describe the fluctuations in the smectic-C
phase; specifically the effect of the tilt on the wave-vector dependence of the
thermal fluctuations must be explicitly taken into account. Both the magnitude
and the temperature dependence of the smectic-C tilt order parameter are
observed to be unaffected by the disorder. This may be a consequence of the
large bare smectic correlation length in the direction of modulation for this
transition. These results show that the understanding developed for the nematic
to smectic-A transition for octylcyanobiphenyl (8CB) and octyloxycyanobiphenyl
(8OCB) liquid crystals with quenched disorder can be extended to quite
different materials and transitions.Comment: 7 pages, 8 figure
Three-algebra for supermembrane and two-algebra for superstring
While string or Yang-Mills theories are based on Lie algebra or two-algebra
structure, recent studies indicate that M-theory may require a one higher,
three-algebra structure. Here we construct a covariant action for a
supermembrane in eleven dimensions, which is invariant under global
supersymmetry, local fermionic symmetry and worldvolume diffeomorphism. Our
action is classically on-shell equivalent to the celebrated
Bergshoeff-Sezgin-Townsend action. However, the novelty is that we spell the
action genuinely in terms of Nambu three-brackets: All the derivatives appear
through Nambu brackets and hence it manifests the three-algebra structure.
Further the double dimensional reduction of our action gives straightforwardly
to a type IIA string action featuring two-algebra. Applying the same method, we
also construct a covariant action for type IIB superstring, leading directly to
the IKKT matrix model.Comment: 1+15 pages, no figure; Refs added, Accepted for publication in JHE
Supersymmetric Heterotic Action out of M5 Brane
Generalizing the work by Cherkis and Schwarz [1], we carry out the double
dimensional reduction of supersymmetric M5 brane on K3 to obtain the
supersymmetric action of heterotic string in 7-dimensional flat space-time.
Motivated by this result, we propose the supersymmetric heterotic action in
10-dimensional flat space-time where the current algebra is realized in a novel
way. We explicitly verify the kappa-symmetry of the proposed action.Comment: 27 page
Electromigration-Induced Flow of Islands and Voids on the Cu(001) Surface
Electromigration-induced flow of islands and voids on the Cu(001) surface is
studied at the atomic scale. The basic drift mechanisms are identified using a
complete set of energy barriers for adatom hopping on the Cu(001) surface,
combined with kinetic Monte Carlo simulations. The energy barriers are
calculated by the embedded atom method, and parameterized using a simple model.
The dependence of the flow on the temperature, the size of the clusters, and
the strength of the applied field is obtained. For both islands and voids it is
found that edge diffusion is the dominant mass-transport mechanism. The rate
limiting steps are identified. For both islands and voids they involve
detachment of atoms from corners into the adjacent edge. The energy barriers
for these moves are found to be in good agreement with the activation energy
for island/void drift obtained from Arrhenius analysis of the simulation
results. The relevance of the results to other FCC(001) metal surfaces and
their experimental implications are discussed.Comment: 9 pages, 13 ps figure
Thermodynamics of a black hole based on a generalized uncertainty principle
We study thermodynamic quantities and the stability of a black hole in a
cavity using the Euclidean action formalism by Gibbons and Hawking based on the
generalized uncertainty relation which is extended in a symmetric way with
respect to the space and momentum without loss of generality. Two parameters in
the uncertainty relation affect the thermodynamical quantities such as energy,
entropy, and the heat capacity. In particular, it can be shown that the small
black hole is unstable and it may decay either into a minimal black hole or a
large black hole. We discuss a constraint for a large black hole comparable to
the size of the cavity in connection with the critical mass.Comment: 12 pages, 4 figures; v2. to appear in JHE
Observation of the Smectic C -- Smectic I Critical Point
We report the first observation of the smectic C--smectic I (C--I) critical
point by Xray diffraction studies on a binary system. This is in confirmity
with the theoretical idea of Nelson and Halperin that coupling to the molecular
tilt should induce hexatic order even in the C phase and as such both C and I
(a tilted hexatic phase) should have the same symmetry. The results provide
evidence in support of the recent theory of Defontaines and Prost proposing a
new universality class for critical points in layered systems.Comment: 9 pages Latex and 5 postscript figures available from
[email protected] on request, Phys.Rev.Lett. (in press
Four-point functions in N=2 superconformal field theories
Four-point correlation functions of hypermultiplet bilinear composites are
analysed in N=2 superconformal field theory using the superconformal Ward
identities and the analyticity properties of the composite operator
superfields. It is shown that the complete amplitude is determined by a single
arbitrary function of the two conformal cross-ratios of the space-time
variables.Comment: 36 pp LaTeX2e, uses amsfonts, amssymb. Some references adde
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